diff --git a/mindplot/src/main/javascript/Designer.js b/mindplot/src/main/javascript/Designer.js
index 5dba0316..60b74cee 100644
--- a/mindplot/src/main/javascript/Designer.js
+++ b/mindplot/src/main/javascript/Designer.js
@@ -590,6 +590,7 @@ mindplot.Designer = new Class({
             var validateFunc = function(topic) {
                 return !(topic.getType() == mindplot.model.INodeModel.CENTRAL_TOPIC_TYPE && shape == mindplot.model.INodeModel.SHAPE_TYPE_LINE)
             };
+
             var validateError = 'Central Topic shape can not be changed to line figure.';
             var topicsIds = this.getModel().filterTopicsIds(validateFunc, validateError);
             if (topicsIds.length > 0) {
diff --git a/mindplot/src/main/javascript/commands/AddIconToTopicCommand.js b/mindplot/src/main/javascript/commands/AddIconToTopicCommand.js
index af86414f..2b3a556d 100644
--- a/mindplot/src/main/javascript/commands/AddIconToTopicCommand.js
+++ b/mindplot/src/main/javascript/commands/AddIconToTopicCommand.js
@@ -19,7 +19,7 @@
 mindplot.commands.AddIconToTopicCommand = new Class({
     Extends:mindplot.Command,
     initialize: function(topicId, iconType) {
-        $assert(topicId, 'topicId can not be null');
+        $assert($defined(topicId), 'topicId can not be null');
         $assert(iconType, 'iconType can not be null');
         this._objectsIds = topicId;
         this._iconType = iconType;
diff --git a/mindplot/src/main/javascript/model/Mindmap.js b/mindplot/src/main/javascript/model/Mindmap.js
index 4af2df40..60f200d1 100644
--- a/mindplot/src/main/javascript/model/Mindmap.js
+++ b/mindplot/src/main/javascript/model/Mindmap.js
@@ -95,11 +95,11 @@ mindplot.model.Mindmap = new Class({
             return new mindplot.model.NodeModel(type, this, id);
         },
 
-        createRelationship : function(fromNode, toNode) {
-            $assert(fromNode, 'from node cannot be null');
-            $assert(toNode, 'to node cannot be null');
+        createRelationship : function(sourceNodeId, targetNodeId) {
+            $assert($defined(sourceNodeId), 'from node cannot be null');
+            $assert($defined(targetNodeId), 'to node cannot be null');
 
-            return new mindplot.model.RelationshipModel(fromNode, toNode);
+            return new mindplot.model.RelationshipModel(sourceNodeId, targetNodeId);
         },
 
         addRelationship : function(relationship) {
diff --git a/mindplot/src/main/javascript/model/RelationshipModel.js b/mindplot/src/main/javascript/model/RelationshipModel.js
index 13b14f01..f0e6b85a 100644
--- a/mindplot/src/main/javascript/model/RelationshipModel.js
+++ b/mindplot/src/main/javascript/model/RelationshipModel.js
@@ -16,13 +16,13 @@
  *   limitations under the License.
  */
 mindplot.model.RelationshipModel = new Class({
-    initialize:function(fromNode, toNode) {
-        $assert(fromNode, 'from node type can not be null');
-        $assert(toNode, 'to node type can not be null');
+    initialize:function(sourceTopicId, targetTopicId) {
+        $assert($defined(sourceTopicId), 'from node type can not be null');
+        $assert($defined(targetTopicId), 'to node type can not be null');
 
         this._id = mindplot.model.RelationshipModel._nextUUID();
-        this._fromNode = fromNode;
-        this._toNode = toNode;
+        this._sourceTargetId = sourceTopicId;
+        this._targetTopicId = targetTopicId;
         this._lineType = mindplot.ConnectionLine.SIMPLE_CURVED;
         this._srcCtrlPoint = null;
         this._destCtrlPoint = null;
@@ -31,11 +31,11 @@ mindplot.model.RelationshipModel = new Class({
     },
 
     getFromNode : function() {
-        return this._fromNode;
+        return this._sourceTargetId;
     },
 
     getToNode : function() {
-        return this._toNode;
+        return this._targetTopicId;
     },
 
     getId : function() {
@@ -83,7 +83,7 @@ mindplot.model.RelationshipModel = new Class({
     },
 
     clone : function(model) {
-        var result = new mindplot.model.RelationshipModel(this._fromNode, this._toNode);
+        var result = new mindplot.model.RelationshipModel(this._sourceTargetId, this._targetTopicId);
         result._id = this._id;
         result._lineType = this._lineType;
         result._srcCtrlPoint = this._srcCtrlPoint;