Workflow designer error- ArgumentNullException: Value cannot be null



Scenario: I was trying to copy and move several sequences/flowcharts, and then an error occurred.

Argumentnullexception: Value cannot be null. Parameter name: key

Current Behavior: Main workflow not displaying.

Expected Behavior: Main workflow visible

Studio/Robot/Orchestrator Version: 2016.2.6379

Last stable behavior:
Last stable version:
OS Version:
Others if Relevant: (workflow, logs, .net version, service pack, etc):


The error here is quite clear something you are referencing is not set.

This could be one of the following:

  1. an argument in or out of a workflow
  2. a variable within a workflow
  3. a value you are passing to a method
  4. a property you are passing to an activity.

You would need to provide more information about the variables/activities you are working with.



Hello, were you able to resolve this issue, I am also facing the same error.


Hi, turns out there was a missing argument in one of the activities I used. I cannot edit the workflow so I just redo the whole thing.