delete a merged pull request return 500

[lunny]

exit status 1 - error: cannot lock ref 'refs/pull/2': 'refs/pull/2/head' exists; cannot create 'refs/pull/2'
 - error: cannot lock ref 'refs/pull/2': 'refs/pull/2/head' exists; cannot create 'refs/pull/2'

[a1012112796]

we can delete pull request now?

[lunny]

Yes.

[a1012112796]

I see. ref: #18879