Fix for a minor bug whereby a new, empty custom field would appear with a ''deleted'' message on first ticket comment on existing tickets as it picked up a change from `None` to `''` (empty string).
Fix for a minor bug whereby a new, empty custom field would appear with a ''deleted'' message on first ticket comment on existing tickets as it picked up a change from `None` to `''` (empty string).

Ticket and patch on #4447 by thatch.

git-svn-id: 0d96b0c1a6983ccc08b3732614f4d6bfcf9cbb42@6330 af82e41b-90c4-0310-8c96-b1721e28e2e2

rbaumg/trac,rbaumg/trac,rbaumg/trac,rbaumg/trac