Copying only parent value from the cascading field to another field in the same issue.in Jira server

[vikranthcms]

From the existing Cascading select field I need to identify and copy only the parent value to another select text field.

Ex: Cascading field is F1 and text filed is F2

F1 values Parent P1has Childvalues as  C1,C2,C3 & Parent P2 has C4,c5,c6 as the child values.

If I Select F1 value as P1 and No child values is selected(the default None ) then I need to copy the Parent value to F2 field.