RoslynExpressionEditor throws NullReferenceException when triggered from IActivityTemplateFactory

[cloudhack]

If you add an activity that implements IActivityTemplateFactory ( ForEach Activity for instance ) the editor throws an NullReferenceException at CreateExpressionEditor
( if you clear the declaredVariables list, you wont get the NullReferenceException any more, but then intellisense will not work )

I think the error happens in UpdateInstance in the RoslynExpressionEditorInstance
This ugly hack, seemed to solve the issue for me

` variableDeclarations = string.Join("", variables.Select(v => {
var c = v.GetCurrentValue() as System.Activities.Variable;
if (c != null) return c.Type.FullName + " " + c.Name + ";\n";
var d = v.GetCurrentValue() as System.Activities.DelegateArgument;
if (d != null) return d.Type.FullName + " " + d.Name + ";\n";
return null;
//return d.Type.FullName + " " + d.Name + ";\n";
}).ToArray());

`