Unable to duplicate a plan in Advanced Roadmap due to Trashed custom field

Issue Summary

Unable to create a duplicate plan in Advanced Roadmap, Getting the below error when trying to duplicate the plan:

couldn't duplicate your plan. Try again.

Steps to Reproduce

1. Create 'Plan A' in Advanced Roadmap
2. Move one of the Custom Fields used in the plan to 'Trash'
3. Try creating a duplicate plan for 'Plan A'
4. It fails with an error - couldn't duplicate your plan. Try again.

Expected Results

The UI should show a clear message that as the particular "XYZ" custom field exists in the trash, the duplicate plan creation fails. 

Actual Results

The below exception is thrown in the UI:

We couldn't duplicate your plan. Try again.

Workaround

• The customer may either delete the custom field permanently or have it restored. 
• Once this action is performed, you should be able to duplicate the plan without any hindrance.