Unexpected runtime error

The runtime has encountered an unexpected error.

Error source

Page Name:/start.xsp
Control Id: _id34

Exception

com.ibm.xsp.exception.EvaluationExceptionEx: Error while executing JavaScript computed expression
Error while executing JavaScript computed expression
Script interpreter error, line=6, col=40: 'userDoc' is null

JavaScript code

   1: 
   2: 					
   3: 			var db:NotesDatabase = session.getCurrentDatabase();
   4: 			var vw:NotesView = db.getView('lu');
   5: 			var userDoc:NotesDocument = vw.getDocumentByKey(param.c);
   6: 			return userDoc.getUniversalID();
   7: 						
   8: 			 

Stack Trace