NullPointerException when resolving a non-existent commit

[Vampire]

I tried to get a non-existent commit.
In my case it was HEAD on an orphaned branch where naturally no head reference is present, the same should happen on a newly initialized repository though.
In that situation I called Grgit.head() which resulted in the following exception:

Caused by: java.lang.NullPointerException
        at org.eclipse.jgit.lib.Repository.resolve(Repository.java:531)
        at org.eclipse.jgit.lib.Repository.resolve(Repository.java:492)
        at org.eclipse.jgit.lib.Repository$resolve.call(Unknown Source)
        at org.eclipse.jgit.lib.Repository$resolve.call(Unknown Source)
        at org.ajoberstar.grgit.util.JGitUtil.resolveObject(JGitUtil.groovy:43)
        at org.ajoberstar.grgit.util.JGitUtil.resolveCommit(JGitUtil.groovy:86)
        at org.ajoberstar.grgit.util.JGitUtil$resolveCommit$0.callStatic(Unknown Source)
        at org.ajoberstar.grgit.util.JGitUtil.resolveCommit(JGitUtil.groovy:87)
        at org.ajoberstar.grgit.util.JGitUtil$resolveCommit$0.call(Unknown Source)
        at org.ajoberstar.grgit.service.ResolveService.toCommit(ResolveService.groovy:78)
        at org.ajoberstar.grgit.service.ResolveService$toCommit.call(Unknown Source)
        at org.ajoberstar.grgit.Grgit.head(Grgit.groovy:138)

The reason is in org.ajoberstar.grgit.util.JGitUtil#resolveCommit(org.ajoberstar.grgit.Repository, java.lang.String):

  static Commit resolveCommit(Repository repo, String revstr) {
    ObjectId id = resolveObject(repo, revstr)
    return resolveCommit(repo, id)
  }

resolveObject for a string that cannot be resolved to an object id returns null according to situation and also its JavaDoc.
resolveCommit(repo, id) then recursively calls itself (not the object id overload like it would be in Java) which then results in the call resolveObject(repo, null) which then ultimately throws the NullPointerException.

I guess the correct fix would be

  static Commit resolveCommit(Repository repo, String revstr) {
    ObjectId id = resolveObject(repo, revstr)
    return id ? resolveCommit(repo, id) : null
  }

[ajoberstar]

Thanks for reporting, will fix in next release.