Summary:
Fix a regression introduced here:
96ae4ba13a
I reproduced this exception executing "svn commit" on a hosted repository.
That crash happened because the PHP getenv() function can return false.
But, that is a very terrible value that blasts the non-string-empty check.
So, now the default getenv() value is skipped, without causing problems.
Closes T15253
Ref T15190
Test Plan: - I've run `svn commit` and I have not encountered any issue now
Reviewers: O1 Blessed Committers, avivey
Reviewed By: O1 Blessed Committers, avivey
Subscribers: speck, tobiaswiese, Matthew, Cigaryno
Maniphest Tasks: T15253, T15190
Differential Revision: https://we.phorge.it/D25122
a5c93dea56