diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Drawing/NodeControl.xaml.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Drawing/NodeControl.xaml.cs
index 993ef83f94..946d73eb0f 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Drawing/NodeControl.xaml.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Drawing/NodeControl.xaml.cs
@@ -67,7 +67,7 @@ namespace Debugger.AddIn.Visualizers.Graph.Drawing
 			var row = new RowDefinition();
 			propertyGrid.RowDefinitions.Add(row);
 			
-			if (!property.IsAtomic)
+			if (!property.IsAtomic && !property.IsNull)
 			{
 				Button btnExpandCollapse = new Button();
 				btnExpandCollapse.Tag = property;
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ExpandedNodes.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ExpandedNodes.cs
index 8f29e49dde..8dc6dbb28d 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ExpandedNodes.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ExpandedNodes.cs
@@ -25,12 +25,12 @@ namespace Debugger.AddIn.Visualizers.Graph
 			return expandedNodes.ContainsKey(expression) && (expandedNodes[expression] == true);
 		}
 		
-		public void Expand(string expression)
+		public void SetExpanded(string expression)
 		{
 			expandedNodes[expression] = true;
 		}
 		
-		public void Collapse(string expression)
+		public void SetCollapsed(string expression)
 		{
 			expandedNodes[expression] = false;
 		}
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/PositionedNodeProperty.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/PositionedNodeProperty.cs
index 85fc4ac103..596b4087e1 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/PositionedNodeProperty.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/PositionedNodeProperty.cs
@@ -67,5 +67,10 @@ namespace Debugger.AddIn.Visualizers.Graph.Layout
         /// Is this property of atomic type? (int, string, etc.)
         /// </summary>
 		public bool IsAtomic { get { return this.objectProperty.IsAtomic; } }
+		
+		/// <summary>
+        /// Is the value of this property null?
+        /// </summary>
+		public bool IsNull { get { return this.objectProperty.IsNull; } }
 	}
 }
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/Tree/NeatoProcess.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/Tree/NeatoProcess.cs
index 78e7f0992e..481e54f704 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/Tree/NeatoProcess.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/Layout/Tree/NeatoProcess.cs
@@ -73,10 +73,10 @@ namespace Debugger.AddIn.Visualizers.Graph.Layout
 		/// <returns>Same graph in Graphviz plain with position information added.</returns>
 		public string CalculatePositions(string dotGraph)
 		{
-			using (var writer = new StreamWriter(@"D:\__prog__\Graphviz\logIn.gv"))
+			/*using (var writer = new StreamWriter("logIn.gv"))
 			{
 				writer.Write(dotGraph);
-			}
+			}*/
 			
 			neatoProcess.StandardInput.Write(dotGraph);
 			neatoProcess.StandardInput.Flush();
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectGraphBuilder.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectGraphBuilder.cs
index 2984c6db57..5daaabf17d 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectGraphBuilder.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectGraphBuilder.cs
@@ -136,7 +136,8 @@ namespace Debugger.AddIn.Visualizers.Graph
 				else
 				{
 					ObjectNode targetNode = null;
-					if (!isNull(memberExpr) && expandedNodes.IsExpanded(memberExpr.Code))
+					bool memberIsNull = isNull(memberExpr);
+					if (!memberIsNull && expandedNodes.IsExpanded(memberExpr.Code))
 					{
 						// for object members, edges are added
 						Value memberValue = getPermanentReference(memberExpr);
@@ -153,7 +154,7 @@ namespace Debugger.AddIn.Visualizers.Graph
 					{
 						targetNode = null;
 					}
-					thisNode.AddComplexProperty(memberName, "", memberExpr, targetNode);
+					thisNode.AddComplexProperty(memberName, "", memberExpr, targetNode, memberIsNull);
 				}
 			}
 			
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectNode.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectNode.cs
index 71ed241064..61ecc65193 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectNode.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectNode.cs
@@ -103,10 +103,10 @@ namespace Debugger.AddIn.Visualizers.Graph
 		/// <summary>
 		/// Adds complex property.
 		/// </summary>
-		internal void AddComplexProperty(string name, string value, Expression expression, ObjectNode targetNode)
+		internal void AddComplexProperty(string name, string value, Expression expression, ObjectNode targetNode, bool isNull)
 		{
 			properties.Add(new ObjectProperty
-			                { Name = name, Value = value, Expression = expression, IsAtomic = false, TargetNode = targetNode });
+			                { Name = name, Value = value, Expression = expression, IsAtomic = false, TargetNode = targetNode, IsNull = isNull });
 		}
 	}
 }
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectProperty.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectProperty.cs
index 52490e4235..b6416bf0e2 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectProperty.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/ObjectGraph/ObjectProperty.cs
@@ -30,14 +30,19 @@ namespace Debugger.AddIn.Visualizers.Graph
         /// </summary>
         public Debugger.Expressions.Expression Expression { get; set; }
         
+        /// <summary>
+        /// Is this property of atomic type? (int, string, etc.)
+        /// </summary>
+        public bool IsAtomic { get; set; }
+        
         /// <summary>
         /// Node that this property points to. Can be null. Always null if <see cref="IsAtomic"/> is true.
         /// </summary>
         public ObjectNode TargetNode { get; set; }
         
         /// <summary>
-        /// Is this property of atomic type? (int, string, etc.)
+        /// Is this property value null? Only meaningful if <see cref="IsAtomic"/> is false.
         /// </summary>
-        public bool IsAtomic { get; set; }
+        public bool IsNull { get; set; }
     }
 }
diff --git a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/VisualizerWPFWindow.xaml.cs b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/VisualizerWPFWindow.xaml.cs
index a8aea03512..08457c8a09 100644
--- a/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/VisualizerWPFWindow.xaml.cs
+++ b/src/AddIns/Misc/Debugger/Debugger.AddIn/Project/Src/Visualizers/Graph/VisualizerWPFWindow.xaml.cs
@@ -146,13 +146,13 @@ namespace Debugger.AddIn.Visualizers.Graph
 
 		void node_Expanded(object sender, PositionedPropertyEventArgs e)
 		{
-			expandedNodes.Expand(e.Property.Expression.Code);
+			expandedNodes.SetExpanded(e.Property.Expression.Code);
 			refreshGraph();
 		}
 		
 		void node_Collapsed(object sender, PositionedPropertyEventArgs e)
 		{
-			expandedNodes.Collapse(e.Property.Expression.Code);
+			expandedNodes.SetCollapsed(e.Property.Expression.Code);
 			refreshGraph();
 		}
     }