NPE in countCommitsSince(branchPoint(...))

[oliver-brm]

Actual behavior:
The branchPoint("unknown") returns null if the specified branch point does not exist (or is not found). Therefore, countCommitsSince(branchPoint("unknown")) may throw a NullPointerException because it currently does not check for null.

Expected behavior:
countCommitsSince should check if the incoming value of obj is null and return -1 if so.

I've provided a fix in Pull Request #4.