How to suspend/hide the description in the parent/main ticket in Jira, but not in its Sub-task

[Sonia]

The issue called "Onboarding" of a project will automatically create a Sub-task (using post functions at transition:create.  We need to put some instructions in the Description field for users to complete the Sub-task.  The content of the description is setup in the Behavior in ScriptRunner. 

Syntax:
===================================

  //  getFieldByName('Description').setHidden(true)   // This line does not work

 //   field.setFieldOptions(['Sub-task'])  //only Subtask is allowed but nothing shows up.

//-------------------------------------------------------------------------------------------------------

def field = getFieldByName('Description')

def defaultValue = """\

      *When onboarding with BSF and setting up its pipeline feature and other capabilities, completing the checklist steps in this Jira ticket should help you through the process.*

     ... etc.

""".stripIndent()

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The content pops up OK in both the parent "Onboarding" and Sub-Task.

Since it is a duplicate content, and I try to omit/hide the description in the main ticket, but there is no way to make it work.  I also try to use new custom field "Onboard Description" for Sub-Task and remove "Description" from the main ticket. The result is no content/blank  for both main and sub-task.

  Please advise how to proceed this?

   Thank you!

   Cathy