Workflow Creation Error

Hi Community,

I created a new flow by clicking new template from the templates page. But the flow gets stuck at the first step and gives an error that it should not give, what could be the reason for this?  Even though I defined all the parameters correctly, nothing changed.

Code:

wt.doc.WTDocument doc = (wt.doc.WTDocument) primaryBusinessObject;

 docNumber=doc.getNumber();
 docName=doc.getName();

 Error:

wt.workflow.engine.FailedExpressionException: wt.util.WTException: java.lang.NullPointerException
Nested exception is: java.lang.NullPointerException
Nested exception is: wt.util.WTException: java.lang.NullPointerException
Nested exception is: java.lang.NullPointerException