fix #361: ApplicationException in code editor related to semantic highlighting

Author: siegfriedpammer

src/AddIns/BackendBindings/CSharpBinding/Project/Src/CSharpSemanticHighlighter.cs

@@ -412,7 +412,7 @@ protected override void Colorize(AstNode node, HighlightingColor color)
 				if (resolverNode.Role == Roles.Type && resolverNode.Parent is ObjectCreateExpression)
 					resolverNode = resolverNode.Parent;
 
-				if (node is Identifier)
+				if (node is Identifier && !node.IsNull)
 					resolverNode.AddAnnotation(node);
 				if (color != null)
 					resolverNode.AddAnnotation(color);