Fixing a crash when the parentCommit is nil.
This happened for me, when I clicked the first commit in a repo. The parentSHA was an empty string. We probably should handle error in some way instead of just logging it.
Suppressing logging if there was an empty parentSHA.
Merge pull request #150 from JanX2/jan/parentCommit-crash-fix

Fixing a crash when the parentCommit is nil.