Problem Definition

Zombie tasks (Task without a parent, and cannot be transitioned ) created during the creation of subtask, when the workflow contains a post function, Copy value from the field in parent task to the subtask.

Please note that the issue is only when the custom field type is Select list (cascading)

Steps to reproduce the issue

• In the Subtask Workflow —> Create issue transition —> Add a post function
• The field (Select list cascade) will take the value from (Select list cascade) Source issue is the parent, destination the sub-task
• Create a Subtask. ( Make sure that the parent task includes the field Select list Cascade)
• During the issue creation, we do observe an error as below.
  
• In spite of the error, an issue is created, which does not have any parent tasks. Also does not have any transition buttons available to it.
• Also this is observed, only when the cascade list option does not have a sub-option. for example in the image below the value PL doesn't have the sub-option. Thus post function fails as it cannot copy a NULL value which None is.
  

  Expected Result

  A subtask should be successfully created, with all the transition options.

Workaround

As a workaround, we would suggest you add the values called 'None' or 'NA', so that the field does have some value. And then the post function can copy the same when creating new issues.