While importing documents via DocuWare Import you get the following error: The object reference was not set to an object instance

Behavior:
If you try to upload a document with DocuWare Import and you also prefill a field with a predefined value (e.g. currentuserlongname) you get the following error:
"The object reference was not set to an instance of an object"

In the log file of the Job Server you will find the following message:
"Object reference not set to an instance of an object.
   at DocuWare.Jobs.Cloud.Activities.PrepareIndexValues.AddStoreDialogValuesForControlStatements(ObservableCollection`1 assignments, RecognitionTargetBase configTarget, IPlatformFacade platform, Boolean configIsUsed)"

Solution:
This behavior only occurs if the field, which should be prefilled, is locked in the store dialog, to solve this behavior the option "Lock Field" has to be disabled for the field in the store dialog.