diff --git a/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementFromJsonVisitor.java b/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementFromJsonVisitor.java
index 81bebb72e..e6059b4dc 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementFromJsonVisitor.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementFromJsonVisitor.java
@@ -1,12 +1,12 @@
 /*
  * Copyright 2015 Robert von Burg <eitch@eitchnet.ch>
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *     http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -23,20 +23,9 @@ import java.util.Set;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
-
 import li.strolch.exception.StrolchException;
-import li.strolch.model.AbstractStrolchElement;
-import li.strolch.model.GroupedParameterizedElement;
-import li.strolch.model.Order;
-import li.strolch.model.ParameterBag;
-import li.strolch.model.ParameterizedElement;
-import li.strolch.model.Resource;
-import li.strolch.model.State;
-import li.strolch.model.StrolchRootElement;
-import li.strolch.model.StrolchValueType;
-import li.strolch.model.Tags;
+import li.strolch.model.*;
 import li.strolch.model.Tags.Json;
-import li.strolch.model.Version;
 import li.strolch.model.activity.Action;
 import li.strolch.model.activity.Activity;
 import li.strolch.model.activity.TimeOrdering;
@@ -71,15 +60,15 @@ public class StrolchElementFromJsonVisitor {
 			order.setPolicyDefs(defs);
 
 		// attributes
-		if (jsonObject.has(Tags.Json.DATE)) {
-			String date = jsonObject.get(Tags.Json.DATE).getAsString();
+		if (jsonObject.has(Json.DATE)) {
+			String date = jsonObject.get(Json.DATE).getAsString();
 			order.setDate(ISO8601FormatFactory.getInstance().getDateFormat().parse(date));
 		} else {
 			order.setDate(ISO8601FormatFactory.getInstance().getDateFormat().parse(StringHelper.DASH)); //$NON-NLS-1$
 		}
 
-		if (jsonObject.has(Tags.Json.STATE)) {
-			order.setState(State.parse(jsonObject.get(Tags.Json.STATE).getAsString()));
+		if (jsonObject.has(Json.STATE)) {
+			order.setState(State.parse(jsonObject.get(Json.STATE).getAsString()));
 		} else {
 			order.setState(State.CREATED);
 		}
@@ -101,10 +90,10 @@ public class StrolchElementFromJsonVisitor {
 			resource.setPolicyDefs(defs);
 
 		// time states
-		if (!jsonObject.has(Tags.Json.TIMED_STATES))
+		if (!jsonObject.has(Json.TIMED_STATES))
 			return;
 
-		JsonObject timedStatesJ = jsonObject.getAsJsonObject(Tags.Json.TIMED_STATES);
+		JsonObject timedStatesJ = jsonObject.getAsJsonObject(Json.TIMED_STATES);
 		Set<Entry<String, JsonElement>> entrySet = timedStatesJ.entrySet();
 		for (Entry<String, JsonElement> entry : entrySet) {
 
@@ -112,7 +101,7 @@ public class StrolchElementFromJsonVisitor {
 			JsonObject timeStateJ = entry.getValue().getAsJsonObject();
 
 			// evaluate type of TimedState
-			String typeS = timeStateJ.get(Tags.Json.TYPE).getAsString();
+			String typeS = timeStateJ.get(Json.TYPE).getAsString();
 			DBC.PRE.assertNotEmpty("Type must be set on TimedState for resource with id " + resource.getId(), typeS);
 			StrolchValueType valueType = StrolchValueType.parse(typeS);
 			StrolchTimedState<? extends IValue<?>> timedState = valueType.timedStateInstance();
@@ -128,29 +117,29 @@ public class StrolchElementFromJsonVisitor {
 			}
 
 			// further attributes
-			if (timeStateJ.has(Tags.Json.INTERPRETATION))
-				timedState.setInterpretation(timeStateJ.get(Tags.Json.INTERPRETATION).getAsString());
-			if (timeStateJ.has(Tags.Json.UOM))
-				timedState.setUom(timeStateJ.get(Tags.Json.UOM).getAsString());
-			if (timeStateJ.has(Tags.Json.INDEX))
-				timedState.setIndex(timeStateJ.get(Tags.Json.INDEX).getAsInt());
-			if (timeStateJ.has(Tags.Json.HIDDEN))
-				timedState.setHidden(timeStateJ.get(Tags.Json.HIDDEN).getAsBoolean());
+			if (timeStateJ.has(Json.INTERPRETATION))
+				timedState.setInterpretation(timeStateJ.get(Json.INTERPRETATION).getAsString());
+			if (timeStateJ.has(Json.UOM))
+				timedState.setUom(timeStateJ.get(Json.UOM).getAsString());
+			if (timeStateJ.has(Json.INDEX))
+				timedState.setIndex(timeStateJ.get(Json.INDEX).getAsInt());
+			if (timeStateJ.has(Json.HIDDEN))
+				timedState.setHidden(timeStateJ.get(Json.HIDDEN).getAsBoolean());
 
 			resource.addTimedState(timedState);
 
-			if (!timeStateJ.has(Tags.Json.VALUES))
+			if (!timeStateJ.has(Json.VALUES))
 				continue;
 
-			JsonArray valuesJ = timeStateJ.getAsJsonArray(Tags.Json.VALUES);
+			JsonArray valuesJ = timeStateJ.getAsJsonArray(Json.VALUES);
 			valuesJ.forEach(e -> {
 
 				JsonObject timeValueJ = e.getAsJsonObject();
 
-				String timeS = timeValueJ.get(Tags.Json.TIME).getAsString();
+				String timeS = timeValueJ.get(Json.TIME).getAsString();
 				long time = ISO8601FormatFactory.getInstance().parseDate(timeS).getTime();
 
-				String valueS = timeValueJ.get(Tags.Json.VALUE).getAsString();
+				String valueS = timeValueJ.get(Json.VALUE).getAsString();
 				timedState.setStateFromStringAt(time, valueS);
 			});
 		}
@@ -164,9 +153,9 @@ public class StrolchElementFromJsonVisitor {
 
 		fillElement(jsonObject, (GroupedParameterizedElement) activity);
 
-		if (!jsonObject.has(Tags.Json.TIME_ORDERING))
+		if (!jsonObject.has(Json.TIME_ORDERING))
 			throw new StrolchException("TimeOrdering not set on " + activity.getLocator());
-		String timeOrderingS = jsonObject.get(Tags.Json.TIME_ORDERING).getAsString();
+		String timeOrderingS = jsonObject.get(Json.TIME_ORDERING).getAsString();
 		TimeOrdering timeOrdering = TimeOrdering.parse(timeOrderingS);
 		activity.setTimeOrdering(timeOrdering);
 
@@ -177,23 +166,23 @@ public class StrolchElementFromJsonVisitor {
 		if (defs.hasPolicyDefs())
 			activity.setPolicyDefs(defs);
 
-		if (!jsonObject.has(Tags.Json.ELEMENTS))
+		if (!jsonObject.has(Json.ELEMENTS))
 			return;
 
-		JsonArray elementsJsonArray = jsonObject.getAsJsonArray(Tags.Json.ELEMENTS);
+		JsonArray elementsJsonArray = jsonObject.getAsJsonArray(Json.ELEMENTS);
 		elementsJsonArray.forEach(e -> {
 
 			JsonObject elementJsonObject = e.getAsJsonObject();
-			String objectType = elementJsonObject.get(Tags.Json.OBJECT_TYPE).getAsString();
+			String objectType = elementJsonObject.get(Json.OBJECT_TYPE).getAsString();
 
 			switch (objectType) {
-			case Tags.Json.ACTIVITY:
+			case Json.ACTIVITY:
 				Activity childActivity = new Activity();
 				fillElement(elementJsonObject, childActivity);
 				activity.addElement(childActivity);
 				break;
 
-			case Tags.Json.ACTION:
+			case Json.ACTION:
 				Action childAction = new Action();
 				fillElement(elementJsonObject, childAction);
 				activity.addElement(childAction);
@@ -208,9 +197,9 @@ public class StrolchElementFromJsonVisitor {
 	}
 
 	protected void fillElement(JsonObject jsonObject, AbstractStrolchElement strolchElement) {
-		if (jsonObject.has(Tags.Json.ID) && jsonObject.has(Tags.Json.NAME)) {
-			strolchElement.setId(jsonObject.get(Tags.Json.ID).getAsString());
-			strolchElement.setName(jsonObject.get(Tags.Json.NAME).getAsString());
+		if (jsonObject.has(Json.ID) && jsonObject.has(Json.NAME)) {
+			strolchElement.setId(jsonObject.get(Json.ID).getAsString());
+			strolchElement.setName(jsonObject.get(Json.NAME).getAsString());
 		} else {
 			String msg = "Check the values of the jsonObject: {0} either id or name attribute is null!"; //$NON-NLS-1$
 			msg = MessageFormat.format(msg, jsonObject);
@@ -221,8 +210,8 @@ public class StrolchElementFromJsonVisitor {
 	protected void fillElement(JsonObject jsonObject, GroupedParameterizedElement groupedParameterizedElement) {
 		fillElement(jsonObject, (AbstractStrolchElement) groupedParameterizedElement);
 
-		if (jsonObject.has(Tags.Json.TYPE)) {
-			groupedParameterizedElement.setType(jsonObject.get(Tags.Json.TYPE).getAsString());
+		if (jsonObject.has(Json.TYPE)) {
+			groupedParameterizedElement.setType(jsonObject.get(Json.TYPE).getAsString());
 		} else {
 			String msg = "Check the values of the jsonObject: {0} type attribute is null!"; //$NON-NLS-1$
 			msg = MessageFormat.format(msg, jsonObject);
@@ -230,10 +219,10 @@ public class StrolchElementFromJsonVisitor {
 		}
 
 		// add all the parameter bags
-		if (!jsonObject.has(Tags.Json.PARAMETER_BAGS))
+		if (!jsonObject.has(Json.PARAMETER_BAGS))
 			return;
 
-		JsonObject bagsJsonObject = jsonObject.getAsJsonObject(Tags.Json.PARAMETER_BAGS);
+		JsonObject bagsJsonObject = jsonObject.getAsJsonObject(Json.PARAMETER_BAGS);
 
 		Set<Entry<String, JsonElement>> bags = bagsJsonObject.entrySet();
 		for (Entry<String, JsonElement> entry : bags) {
@@ -261,8 +250,8 @@ public class StrolchElementFromJsonVisitor {
 	protected void fillElement(JsonObject jsonObject, ParameterizedElement parameterizedElement) {
 		fillElement(jsonObject, (AbstractStrolchElement) parameterizedElement);
 
-		if (jsonObject.has(Tags.Json.TYPE)) {
-			parameterizedElement.setType(jsonObject.get(Tags.Json.TYPE).getAsString());
+		if (jsonObject.has(Json.TYPE)) {
+			parameterizedElement.setType(jsonObject.get(Json.TYPE).getAsString());
 		} else {
 			String msg = "Check the values of the jsonObject: {0} type attribute is null!"; //$NON-NLS-1$
 			msg = MessageFormat.format(msg, jsonObject);
@@ -270,10 +259,10 @@ public class StrolchElementFromJsonVisitor {
 		}
 
 		// add all the parameters
-		if (!jsonObject.has(Tags.Json.PARAMETERS))
+		if (!jsonObject.has(Json.PARAMETERS))
 			return;
 
-		JsonObject parametersJsonObject = jsonObject.getAsJsonObject(Tags.Json.PARAMETERS);
+		JsonObject parametersJsonObject = jsonObject.getAsJsonObject(Json.PARAMETERS);
 		Set<Entry<String, JsonElement>> parameters = parametersJsonObject.entrySet();
 		for (Entry<String, JsonElement> entry : parameters) {
 			String paramId = entry.getKey();
@@ -285,7 +274,7 @@ public class StrolchElementFromJsonVisitor {
 			}
 
 			JsonObject paramJsonObject = jsonElement.getAsJsonObject();
-			String paramtype = paramJsonObject.get(Tags.Json.TYPE).getAsString();
+			String paramtype = paramJsonObject.get(Json.TYPE).getAsString();
 
 			StrolchValueType paramValueType = StrolchValueType.parse(paramtype);
 			Parameter<?> parameter = paramValueType.parameterInstance();
@@ -303,16 +292,16 @@ public class StrolchElementFromJsonVisitor {
 	protected void fillElement(JsonObject jsonObject, Parameter<?> param) {
 		fillElement(jsonObject, (AbstractStrolchElement) param);
 
-		if (jsonObject.has(Tags.Json.INTERPRETATION))
-			param.setInterpretation(jsonObject.get(Tags.Json.INTERPRETATION).getAsString());
-		if (jsonObject.has(Tags.Json.UOM))
-			param.setUom(jsonObject.get(Tags.Json.UOM).getAsString());
-		if (jsonObject.has(Tags.Json.INDEX))
-			param.setIndex(jsonObject.get(Tags.Json.INDEX).getAsInt());
-		if (jsonObject.has(Tags.Json.HIDDEN))
-			param.setHidden(jsonObject.get(Tags.Json.HIDDEN).getAsBoolean());
+		if (jsonObject.has(Json.INTERPRETATION))
+			param.setInterpretation(jsonObject.get(Json.INTERPRETATION).getAsString());
+		if (jsonObject.has(Json.UOM))
+			param.setUom(jsonObject.get(Json.UOM).getAsString());
+		if (jsonObject.has(Json.INDEX))
+			param.setIndex(jsonObject.get(Json.INDEX).getAsInt());
+		if (jsonObject.has(Json.HIDDEN))
+			param.setHidden(jsonObject.get(Json.HIDDEN).getAsBoolean());
 
-		String value = jsonObject.get(Tags.Json.VALUE).getAsString();
+		String value = jsonObject.get(Json.VALUE).getAsString();
 		param.setValueFromString(value);
 	}
 
@@ -320,12 +309,12 @@ public class StrolchElementFromJsonVisitor {
 		fillElement(jsonObject, (GroupedParameterizedElement) action);
 
 		// attributes
-		if (jsonObject.has(Tags.Json.RESOURCE_ID))
-			action.setResourceId(jsonObject.get(Tags.Json.RESOURCE_ID).getAsString());
-		if (jsonObject.has(Tags.Json.RESOURCE_TYPE))
-			action.setResourceType(jsonObject.get(Tags.Json.RESOURCE_TYPE).getAsString());
-		if (jsonObject.has(Tags.Json.STATE))
-			action.setState(State.parse(jsonObject.get(Tags.Json.STATE).getAsString()));
+		if (jsonObject.has(Json.RESOURCE_ID))
+			action.setResourceId(jsonObject.get(Json.RESOURCE_ID).getAsString());
+		if (jsonObject.has(Json.RESOURCE_TYPE))
+			action.setResourceType(jsonObject.get(Json.RESOURCE_TYPE).getAsString());
+		if (jsonObject.has(Json.STATE))
+			action.setState(State.parse(jsonObject.get(Json.STATE).getAsString()));
 
 		// policies
 		PolicyDefs defs = parsePolicies(jsonObject);
@@ -333,18 +322,18 @@ public class StrolchElementFromJsonVisitor {
 			action.setPolicyDefs(defs);
 
 		// value changes
-		if (!jsonObject.has(Tags.Json.VALUE_CHANGES))
+		if (!jsonObject.has(Json.VALUE_CHANGES))
 			return;
 
-		JsonArray valueChangesJ = jsonObject.getAsJsonArray(Tags.Json.VALUE_CHANGES);
+		JsonArray valueChangesJ = jsonObject.getAsJsonArray(Json.VALUE_CHANGES);
 		valueChangesJ.forEach(e -> {
 			try {
 				JsonObject valueChangeJ = e.getAsJsonObject();
 
-				String stateId = valueChangeJ.get(Tags.Json.STATE_ID).getAsString();
-				String timeS = valueChangeJ.get(Tags.Json.TIME).getAsString();
-				String valueS = valueChangeJ.get(Tags.Json.VALUE).getAsString();
-				String typeS = valueChangeJ.get(Tags.Json.TYPE).getAsString();
+				String stateId = valueChangeJ.has(Json.STATE_ID) ? valueChangeJ.get(Json.STATE_ID).getAsString() : "";
+				String timeS = valueChangeJ.get(Json.TIME).getAsString();
+				String valueS = valueChangeJ.get(Json.VALUE).getAsString();
+				String typeS = valueChangeJ.get(Json.TYPE).getAsString();
 
 				StrolchValueType type = StrolchValueType.parse(typeS);
 				IValue<?> value = type.valueInstance(valueS);
@@ -366,10 +355,10 @@ public class StrolchElementFromJsonVisitor {
 
 		PolicyDefs policyDefs = new PolicyDefs();
 
-		if (!jsonObject.has(Tags.Json.POLICIES))
+		if (!jsonObject.has(Json.POLICIES))
 			return policyDefs;
 
-		JsonObject policiesJsonObject = jsonObject.getAsJsonObject(Tags.Json.POLICIES);
+		JsonObject policiesJsonObject = jsonObject.getAsJsonObject(Json.POLICIES);
 
 		Set<Entry<String, JsonElement>> entrySet = policiesJsonObject.entrySet();
 		for (Entry<String, JsonElement> entry : entrySet) {
@@ -385,16 +374,16 @@ public class StrolchElementFromJsonVisitor {
 
 	protected void parseVersion(StrolchRootElement rootElement, JsonObject jsonObject) {
 
-		if (!jsonObject.has(Tags.Json.VERSION))
+		if (!jsonObject.has(Json.VERSION))
 			return;
 
-		JsonObject versionJ = jsonObject.getAsJsonObject(Tags.Json.VERSION);
+		JsonObject versionJ = jsonObject.getAsJsonObject(Json.VERSION);
 
-		int v = versionJ.get(Tags.Json.VERSION).getAsInt();
-		String createdBy = versionJ.get(Tags.Json.CREATED_BY).getAsString();
-		String createdAtS = versionJ.get(Tags.Json.CREATED_AT).getAsString();
+		int v = versionJ.get(Json.VERSION).getAsInt();
+		String createdBy = versionJ.get(Json.CREATED_BY).getAsString();
+		String createdAtS = versionJ.get(Json.CREATED_AT).getAsString();
 		Date createdAt = ISO8601FormatFactory.getInstance().parseDate(createdAtS);
-		boolean deleted = versionJ.get(Tags.Json.DELETED).getAsBoolean();
+		boolean deleted = versionJ.get(Json.DELETED).getAsBoolean();
 
 		Version version = new Version(rootElement.getLocator(), v, createdBy, createdAt, deleted);
 		rootElement.setVersion(version);
diff --git a/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementToJsonVisitor.java b/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementToJsonVisitor.java
index 25f94c724..fbd2f2ac2 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementToJsonVisitor.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/json/StrolchElementToJsonVisitor.java
@@ -1,5 +1,7 @@
 package li.strolch.model.json;
 
+import static li.strolch.utils.helper.StringHelper.isNotEmpty;
+
 import java.util.*;
 import java.util.Map.Entry;
 import java.util.function.BiConsumer;
@@ -10,6 +12,7 @@ import com.google.gson.JsonObject;
 import com.google.gson.JsonPrimitive;
 import li.strolch.exception.StrolchModelException;
 import li.strolch.model.*;
+import li.strolch.model.Tags.Json;
 import li.strolch.model.activity.Action;
 import li.strolch.model.activity.Activity;
 import li.strolch.model.activity.IActivityElement;
@@ -268,7 +271,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 	protected JsonObject toJson(Resource element) {
 
 		JsonObject rootJ = new JsonObject();
-		rootJ.addProperty(Tags.Json.OBJECT_TYPE, Tags.Json.RESOURCE);
+		rootJ.addProperty(Json.OBJECT_TYPE, Json.RESOURCE);
 
 		toJson(element, rootJ);
 
@@ -286,11 +289,11 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 	protected JsonObject toJson(Order element) {
 
 		JsonObject rootJ = new JsonObject();
-		rootJ.addProperty(Tags.Json.OBJECT_TYPE, Tags.Json.ORDER);
+		rootJ.addProperty(Json.OBJECT_TYPE, Json.ORDER);
 
 		toJson(element, rootJ);
-		rootJ.addProperty(Tags.Json.DATE, formatDate(element.getDate()));
-		rootJ.addProperty(Tags.Json.STATE, element.getState().getName());
+		rootJ.addProperty(Json.DATE, formatDate(element.getDate()));
+		rootJ.addProperty(Json.STATE, element.getState().getName());
 
 		addVersion(element, rootJ);
 		addParameterizedElements(element, rootJ);
@@ -314,13 +317,13 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 
 	protected JsonObject toJson(Activity element, JsonObject rootJ, int currentDepth) {
 
-		rootJ.addProperty(Tags.Json.OBJECT_TYPE, Tags.Json.ACTIVITY);
+		rootJ.addProperty(Json.OBJECT_TYPE, Json.ACTIVITY);
 
 		toJson((AbstractStrolchElement) element, rootJ);
-		rootJ.addProperty(Tags.Json.TIME_ORDERING, element.getTimeOrdering().getName());
-		rootJ.addProperty(Tags.Json.STATE, element.getState().getName());
-		rootJ.addProperty(Tags.Json.START, formatDate(element.getStart()));
-		rootJ.addProperty(Tags.Json.END, formatDate(element.getEnd()));
+		rootJ.addProperty(Json.TIME_ORDERING, element.getTimeOrdering().getName());
+		rootJ.addProperty(Json.STATE, element.getState().getName());
+		rootJ.addProperty(Json.START, formatDate(element.getStart()));
+		rootJ.addProperty(Json.END, formatDate(element.getEnd()));
 
 		if (element.isRootElement())
 			addVersion(element, rootJ);
@@ -337,7 +340,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		if (iter.hasNext()) {
 
 			JsonArray elementsJ = new JsonArray();
-			rootJ.add(Tags.Json.ELEMENTS, elementsJ);
+			rootJ.add(Json.ELEMENTS, elementsJ);
 
 			while (iter.hasNext()) {
 				IActivityElement activityElement = iter.next().getValue();
@@ -360,15 +363,15 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 
 	protected JsonObject toJson(Action element, JsonObject rootJ) {
 
-		rootJ.addProperty(Tags.Json.OBJECT_TYPE, Tags.Json.ACTION);
+		rootJ.addProperty(Json.OBJECT_TYPE, Json.ACTION);
 
 		// attributes
 		toJson((AbstractStrolchElement) element, rootJ);
-		rootJ.addProperty(Tags.Json.RESOURCE_ID, element.getResourceId());
-		rootJ.addProperty(Tags.Json.RESOURCE_TYPE, element.getResourceType());
-		rootJ.addProperty(Tags.Json.STATE, element.getState().getName());
-		rootJ.addProperty(Tags.Json.START, formatDate(element.getStart()));
-		rootJ.addProperty(Tags.Json.END, formatDate(element.getEnd()));
+		rootJ.addProperty(Json.RESOURCE_ID, element.getResourceId());
+		rootJ.addProperty(Json.RESOURCE_TYPE, element.getResourceType());
+		rootJ.addProperty(Json.STATE, element.getState().getName());
+		rootJ.addProperty(Json.START, formatDate(element.getStart()));
+		rootJ.addProperty(Json.END, formatDate(element.getEnd()));
 
 		addParameterizedElements(element, rootJ);
 		addPolicies(element, rootJ);
@@ -381,17 +384,18 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		if (iter.hasNext()) {
 
 			JsonArray changesJ = new JsonArray();
-			rootJ.add(Tags.Json.VALUE_CHANGES, changesJ);
+			rootJ.add(Json.VALUE_CHANGES, changesJ);
 
 			while (iter.hasNext()) {
 				IValueChange<? extends IValue<?>> valueChange = iter.next();
 
 				JsonObject changeJ = new JsonObject();
 
-				changeJ.addProperty(Tags.Json.STATE_ID, valueChange.getStateId());
-				changeJ.addProperty(Tags.Json.TIME, formatDate(valueChange.getTime()));
-				changeJ.addProperty(Tags.Json.VALUE, valueChange.getValue().getValueAsString());
-				changeJ.addProperty(Tags.Json.TYPE, valueChange.getValue().getType());
+				if (isNotEmpty(valueChange.getStateId()))
+					changeJ.addProperty(Json.STATE_ID, valueChange.getStateId());
+				changeJ.addProperty(Json.TIME, formatDate(valueChange.getTime()));
+				changeJ.addProperty(Json.VALUE, valueChange.getValue().getValueAsString());
+				changeJ.addProperty(Json.TYPE, valueChange.getValue().getType());
 
 				changesJ.add(changeJ);
 			}
@@ -409,7 +413,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		PolicyDefs policyDefs = policyContainer.getPolicyDefs();
 
 		JsonObject policyDefsJ = new JsonObject();
-		rootJ.add(Tags.Json.POLICIES, policyDefsJ);
+		rootJ.add(Json.POLICIES, policyDefsJ);
 
 		for (String type : policyDefs.getPolicyTypes()) {
 			PolicyDef policyDef = policyDefs.getPolicyDef(type);
@@ -419,12 +423,12 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 
 	protected JsonObject toJson(AbstractStrolchElement element, JsonObject rootJ) {
 
-		rootJ.addProperty(Tags.Json.ID, element.getId());
+		rootJ.addProperty(Json.ID, element.getId());
 
 		if (!isWithoutElementName())
-			rootJ.addProperty(Tags.Json.NAME, element.getName());
+			rootJ.addProperty(Json.NAME, element.getName());
 
-		rootJ.addProperty(Tags.Json.TYPE, element.getType());
+		rootJ.addProperty(Json.TYPE, element.getType());
 
 		return rootJ;
 	}
@@ -487,7 +491,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 			return;
 
 		JsonObject parameterBagsJ = new JsonObject();
-		rootJ.add(Tags.Json.PARAMETER_BAGS, parameterBagsJ);
+		rootJ.add(Json.PARAMETER_BAGS, parameterBagsJ);
 
 		for (String bagKey : element.getParameterBagKeySet()) {
 			ParameterBag bag = element.getParameterBag(bagKey);
@@ -505,7 +509,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		toJson(bag, bagJ);
 
 		JsonObject paramsJ = new JsonObject();
-		bagJ.add(Tags.Json.PARAMETERS, paramsJ);
+		bagJ.add(Json.PARAMETERS, paramsJ);
 
 		for (String paramKey : bag.getParameterKeySet()) {
 			Parameter<?> param = bag.getParameter(paramKey);
@@ -521,18 +525,18 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		toJson((AbstractStrolchElement) param, paramJ);
 
 		if (!StrolchModelConstants.INTERPRETATION_NONE.equals(param.getInterpretation()))
-			paramJ.addProperty(Tags.Json.INTERPRETATION, param.getInterpretation());
+			paramJ.addProperty(Json.INTERPRETATION, param.getInterpretation());
 
 		if (param.isHidden())
-			paramJ.addProperty(Tags.Json.HIDDEN, param.isHidden());
+			paramJ.addProperty(Json.HIDDEN, param.isHidden());
 
 		if (!StrolchModelConstants.UOM_NONE.equals(param.getUom()))
-			paramJ.addProperty(Tags.Json.UOM, param.getUom());
+			paramJ.addProperty(Json.UOM, param.getUom());
 
 		if (param.getIndex() != 0)
-			paramJ.addProperty(Tags.Json.INDEX, param.getIndex());
+			paramJ.addProperty(Json.INDEX, param.getIndex());
 
-		paramJ.addProperty(Tags.Json.VALUE, param.getValueAsString());
+		paramJ.addProperty(Json.VALUE, param.getValueAsString());
 		return paramJ;
 	}
 
@@ -549,7 +553,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 			return;
 
 		JsonObject timedStatesJ = new JsonObject();
-		rootJ.add(Tags.Json.TIMED_STATES, timedStatesJ);
+		rootJ.add(Json.TIMED_STATES, timedStatesJ);
 
 		for (String stateKey : element.getTimedStateKeySet()) {
 
@@ -591,7 +595,7 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		toJson((AbstractStrolchElement) state, stateJ);
 
 		JsonArray valuesJ = new JsonArray();
-		stateJ.add(Tags.Json.VALUES, valuesJ);
+		stateJ.add(Json.VALUES, valuesJ);
 
 		SortedSet<? extends ITimeValue<? extends IValue<?>>> values = state.getTimeEvolution().getValues();
 		for (ITimeValue<? extends IValue<?>> value : values) {
@@ -602,8 +606,8 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 			Long time = value.getTime();
 			String valueS = value.getValue().getValueAsString();
 
-			valueJ.addProperty(Tags.Json.TIME, formatDate(time));
-			valueJ.addProperty(Tags.Json.VALUE, valueS);
+			valueJ.addProperty(Json.TIME, formatDate(time));
+			valueJ.addProperty(Json.VALUE, valueS);
 		}
 		return stateJ;
 	}
@@ -615,8 +619,8 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		JsonArray arrayJ = new JsonArray();
 		for (ITimeValue<? extends IValue<?>> v : timeEvolution.getValues()) {
 			JsonObject obj = new JsonObject();
-			obj.addProperty(Tags.Json.DATE, ISO8601FormatFactory.getInstance().formatDate(v.getTime()));
-			obj.addProperty(Tags.Json.VALUE, v.getValue().getValueAsString());
+			obj.addProperty(Json.DATE, ISO8601FormatFactory.getInstance().formatDate(v.getTime()));
+			obj.addProperty(Json.VALUE, v.getValue().getValueAsString());
 
 			arrayJ.add(obj);
 		}
@@ -632,11 +636,11 @@ public class StrolchElementToJsonVisitor implements StrolchElementVisitor<JsonEl
 		Version version = element.getVersion();
 
 		JsonObject versionJ = new JsonObject();
-		versionJ.addProperty(Tags.Json.VERSION, version.getVersion());
-		versionJ.addProperty(Tags.Json.CREATED_BY, version.getCreatedBy());
-		versionJ.addProperty(Tags.Json.CREATED_AT, formatDate(version.getCreatedAt()));
-		versionJ.addProperty(Tags.Json.DELETED, version.isDeleted());
-		rootJ.add(Tags.Json.VERSION, versionJ);
+		versionJ.addProperty(Json.VERSION, version.getVersion());
+		versionJ.addProperty(Json.CREATED_BY, version.getCreatedBy());
+		versionJ.addProperty(Json.CREATED_AT, formatDate(version.getCreatedAt()));
+		versionJ.addProperty(Json.DELETED, version.isDeleted());
+		rootJ.add(Json.VERSION, versionJ);
 	}
 
 	private static String formatDate(Date date) {
diff --git a/li.strolch.model/src/main/java/li/strolch/model/timevalue/impl/ValueChange.java b/li.strolch.model/src/main/java/li/strolch/model/timevalue/impl/ValueChange.java
index ef53485e1..bcf62d1c5 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/timevalue/impl/ValueChange.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/timevalue/impl/ValueChange.java
@@ -15,6 +15,8 @@
  */
 package li.strolch.model.timevalue.impl;
 
+import static li.strolch.utils.helper.StringHelper.trimOrEmpty;
+
 import java.io.Serializable;
 
 import li.strolch.model.timevalue.IValue;
@@ -55,7 +57,7 @@ public class ValueChange<T extends IValue> implements IValueChange<T>, Serializa
 	public ValueChange(final Long time, final T value, final String stateId) {
 		this.time = time;
 		this.value = value;
-		this.stateId = stateId;
+		this.stateId = trimOrEmpty(stateId);
 	}
 
 	@Override
diff --git a/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToDomVisitor.java b/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToDomVisitor.java
index 153e111ee..c6b711dcd 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToDomVisitor.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToDomVisitor.java
@@ -1,12 +1,12 @@
 /*
  * Copyright 2015 Robert von Burg <eitch@eitchnet.ch>
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *     http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -15,25 +15,14 @@
  */
 package li.strolch.model.xml;
 
+import static li.strolch.utils.helper.StringHelper.isNotEmpty;
+
+import javax.xml.parsers.DocumentBuilder;
 import java.util.Iterator;
 import java.util.Map.Entry;
 import java.util.SortedSet;
 
-import javax.xml.parsers.DocumentBuilder;
-
-import org.w3c.dom.Document;
-import org.w3c.dom.Element;
-
-import li.strolch.model.AbstractStrolchElement;
-import li.strolch.model.GroupedParameterizedElement;
-import li.strolch.model.Order;
-import li.strolch.model.ParameterBag;
-import li.strolch.model.ParameterizedElement;
-import li.strolch.model.Resource;
-import li.strolch.model.StrolchModelConstants;
-import li.strolch.model.StrolchRootElement;
-import li.strolch.model.Tags;
-import li.strolch.model.Version;
+import li.strolch.model.*;
 import li.strolch.model.activity.Action;
 import li.strolch.model.activity.Activity;
 import li.strolch.model.activity.IActivityElement;
@@ -46,8 +35,9 @@ import li.strolch.model.timevalue.IValue;
 import li.strolch.model.timevalue.IValueChange;
 import li.strolch.model.visitor.StrolchRootElementVisitor;
 import li.strolch.utils.helper.DomUtil;
-import li.strolch.utils.helper.StringHelper;
 import li.strolch.utils.iso8601.ISO8601FormatFactory;
+import org.w3c.dom.Document;
+import org.w3c.dom.Element;
 
 /**
  * @author Robert von Burg <eitch@eitchnet.ch>
@@ -144,9 +134,9 @@ public class StrolchElementToDomVisitor implements StrolchRootElementVisitor<Doc
 		Element element = document.createElement(Tags.ACTION);
 		fillElement(element, action);
 
-		if (StringHelper.isNotEmpty(action.getResourceId()))
+		if (isNotEmpty(action.getResourceId()))
 			element.setAttribute(Tags.RESOURCE_ID, action.getResourceId());
-		if (StringHelper.isNotEmpty(action.getResourceType()))
+		if (isNotEmpty(action.getResourceType()))
 			element.setAttribute(Tags.RESOURCE_TYPE, action.getResourceType());
 
 		element.setAttribute(Tags.STATE, action.getState().getName());
@@ -168,7 +158,8 @@ public class StrolchElementToDomVisitor implements StrolchRootElementVisitor<Doc
 
 	protected Element toDom(IValueChange<? extends IValue<?>> value) {
 		Element element = document.createElement(Tags.VALUE_CHANGE);
-		element.setAttribute(Tags.STATE_ID, value.getStateId());
+		if (isNotEmpty(value.getStateId()))
+			element.setAttribute(Tags.STATE_ID, value.getStateId());
 		element.setAttribute(Tags.TIME, ISO8601FormatFactory.getInstance().formatDate(value.getTime()));
 		element.setAttribute(Tags.VALUE, value.getValue().getValueAsString());
 		element.setAttribute(Tags.TYPE, value.getValue().getType());
diff --git a/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxVisitor.java b/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxVisitor.java
index 9aacb13f9..c46ada973 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxVisitor.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxVisitor.java
@@ -17,6 +17,7 @@ package li.strolch.model.xml;
 
 import static li.strolch.model.StrolchModelConstants.INTERPRETATION_NONE;
 import static li.strolch.model.StrolchModelConstants.UOM_NONE;
+import static li.strolch.utils.helper.StringHelper.isNotEmpty;
 
 import java.text.MessageFormat;
 import java.util.Iterator;
@@ -24,19 +25,7 @@ import java.util.Map.Entry;
 import java.util.Set;
 import java.util.SortedSet;
 
-import org.xml.sax.Attributes;
-import org.xml.sax.ContentHandler;
-import org.xml.sax.SAXException;
-import org.xml.sax.helpers.AttributesImpl;
-
-import li.strolch.model.GroupedParameterizedElement;
-import li.strolch.model.Order;
-import li.strolch.model.ParameterBag;
-import li.strolch.model.Resource;
-import li.strolch.model.StrolchElement;
-import li.strolch.model.StrolchRootElement;
-import li.strolch.model.Tags;
-import li.strolch.model.Version;
+import li.strolch.model.*;
 import li.strolch.model.activity.Action;
 import li.strolch.model.activity.Activity;
 import li.strolch.model.activity.IActivityElement;
@@ -48,8 +37,11 @@ import li.strolch.model.timevalue.ITimeValue;
 import li.strolch.model.timevalue.IValue;
 import li.strolch.model.timevalue.IValueChange;
 import li.strolch.model.visitor.StrolchRootElementVisitor;
-import li.strolch.utils.helper.StringHelper;
 import li.strolch.utils.iso8601.ISO8601FormatFactory;
+import org.xml.sax.Attributes;
+import org.xml.sax.ContentHandler;
+import org.xml.sax.SAXException;
+import org.xml.sax.helpers.AttributesImpl;
 
 /**
  * @author Robert von Burg <eitch@eitchnet.ch>
@@ -328,10 +320,10 @@ public class StrolchElementToSaxVisitor implements StrolchRootElementVisitor<Voi
 	protected AttributesImpl attributesFor(Action action) {
 		AttributesImpl attributes = attributesFor((StrolchElement) action);
 
-		if (StringHelper.isNotEmpty(action.getResourceId()))
+		if (isNotEmpty(action.getResourceId()))
 			attributes.addAttribute(null, null, Tags.RESOURCE_ID, Tags.CDATA, action.getResourceId());
 
-		if (StringHelper.isNotEmpty(action.getResourceType()))
+		if (isNotEmpty(action.getResourceType()))
 			attributes.addAttribute(null, null, Tags.RESOURCE_TYPE, Tags.CDATA, action.getResourceType());
 
 		if (!action.getState().isCreated())
@@ -343,7 +335,7 @@ public class StrolchElementToSaxVisitor implements StrolchRootElementVisitor<Voi
 	protected AttributesImpl attributesFor(IValueChange<? extends IValue<?>> valueChange) {
 		AttributesImpl attributes = new AttributesImpl();
 
-		if (StringHelper.isNotEmpty(valueChange.getStateId()))
+		if (isNotEmpty(valueChange.getStateId()))
 			attributes.addAttribute(null, null, Tags.STATE_ID, Tags.CDATA, valueChange.getStateId());
 
 		attributes.addAttribute(null, null, Tags.TIME, Tags.CDATA,
diff --git a/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxWriterVisitor.java b/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxWriterVisitor.java
index fefc07dd4..872e14ed3 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxWriterVisitor.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/xml/StrolchElementToSaxWriterVisitor.java
@@ -17,6 +17,7 @@ package li.strolch.model.xml;
 
 import static li.strolch.model.StrolchModelConstants.INTERPRETATION_NONE;
 import static li.strolch.model.StrolchModelConstants.UOM_NONE;
+import static li.strolch.utils.helper.StringHelper.isNotEmpty;
 
 import javax.xml.stream.XMLStreamException;
 import javax.xml.stream.XMLStreamWriter;
@@ -38,7 +39,6 @@ import li.strolch.model.timevalue.ITimeVariable;
 import li.strolch.model.timevalue.IValue;
 import li.strolch.model.timevalue.IValueChange;
 import li.strolch.model.visitor.StrolchRootElementVisitor;
-import li.strolch.utils.helper.StringHelper;
 import li.strolch.utils.iso8601.ISO8601FormatFactory;
 
 /**
@@ -186,9 +186,9 @@ public class StrolchElementToSaxWriterVisitor implements StrolchRootElementVisit
 
 		writeStartStrolchElement(Tags.ACTION, empty, action);
 		this.writer.writeAttribute(Tags.STATE, action.getState().getName());
-		if (StringHelper.isNotEmpty(action.getResourceId()))
+		if (isNotEmpty(action.getResourceId()))
 			this.writer.writeAttribute(Tags.RESOURCE_ID, action.getResourceId());
-		if (StringHelper.isNotEmpty(action.getResourceType()))
+		if (isNotEmpty(action.getResourceType()))
 			this.writer.writeAttribute(Tags.RESOURCE_TYPE, action.getResourceType());
 
 		if (action.hasParameterBags())
@@ -197,7 +197,8 @@ public class StrolchElementToSaxWriterVisitor implements StrolchRootElementVisit
 		if (action.hasChanges()) {
 			for (IValueChange<? extends IValue<?>> change : action.getChanges()) {
 				this.writer.writeEmptyElement(Tags.VALUE_CHANGE);
-				this.writer.writeAttribute(Tags.STATE_ID, change.getStateId());
+				if (isNotEmpty(change.getStateId()))
+					this.writer.writeAttribute(Tags.STATE_ID, change.getStateId());
 				this.writer.writeAttribute(Tags.TIME, ISO8601FormatFactory.getInstance().formatDate(change.getTime()));
 				this.writer.writeAttribute(Tags.VALUE, change.getValue().getValueAsString());
 				this.writer.writeAttribute(Tags.TYPE, change.getValue().getType());
diff --git a/li.strolch.model/src/main/java/li/strolch/model/xml/XmlModelSaxReader.java b/li.strolch.model/src/main/java/li/strolch/model/xml/XmlModelSaxReader.java
index 97777238b..5c614e729 100644
--- a/li.strolch.model/src/main/java/li/strolch/model/xml/XmlModelSaxReader.java
+++ b/li.strolch.model/src/main/java/li/strolch/model/xml/XmlModelSaxReader.java
@@ -1,12 +1,12 @@
 /*
  * Copyright 2013 Robert von Burg <eitch@eitchnet.ch>
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *     http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.