Post-3.0.13 optional variables cannot be nil

[cqin5]

Description

Has there been any major change after 3.0.13? Our protobuf files worked perfectly with optional variable giving nil properly until we tried updating the version this summer, and we have been trying compiling the file with succeeding versions but none (other than 3.0.13) has worked.

All post-3.0.13 versions crash the app when an optional variable is nil.

[shinma]

I'm also interested in fixing this issue.