When retrieving a machine property in the Workflow Designer of vCAC that does not exist and later on access the internal workflow variable holding that machine property value you will receive a “System.NullReferenceException”.
[UTC:21/07/13 13:11:30.255 Local:21/07 15:11] [Error]: <?xml version="1.0" encoding="utf-16"?> <boolean>false</boolean> Workflow "WFStubMachineProvisioned" failed with the following exception: System.NullReferenceException: Object reference not set to an instance of an object. at lambda_method(Closure , ActivityContext ) at Microsoft.VisualBasic.Activities.VisualBasicValue`1.Execute(CodeActivityContext context) at System.Activities.CodeActivity`1.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager) at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation)
When using a “TryCatch” activity to react upon this condition an exception is only triggered when you set “Is Required” to “True” (regardless of what you defined in your catch block).
As a workaround for you can also pre-initialise the variables in your workflow and then you might not have to use the “TryCatch” activity at all.