Fix posting changes with an empty commit ID.
Review Request #6219 — Created Aug. 12, 2014 and submitted
Posting with an empty commit ID (a blank string) resulted in the blank
string being set for the review request or draft. This resulted in
conflicts, since a blank string is considered a valid value for unique
constraints. We now normalize it to None in this case.
Unit tests pass.
Tool: Pyflakes Processed Files: reviewboard/webapi/tests/test_review_request_draft.py reviewboard/webapi/resources/review_request_draft.py reviewboard/webapi/resources/review_request.py reviewboard/webapi/tests/test_review_request.py Tool: PEP8 Style Checker Processed Files: reviewboard/webapi/tests/test_review_request_draft.py reviewboard/webapi/resources/review_request_draft.py reviewboard/webapi/resources/review_request.py reviewboard/webapi/tests/test_review_request.py