Program: 91288
Project: 91288
Buggy source:
/** 
 * Executes the   {@code Reset} command. Each instance of this class shouldonly be used for one invocation of the command. Don't call this method twice on an instance.
 * @return the Ref after reset
 * @throws GitAPIException
 */
public Ref call() throws GitAPIException, CheckoutConflictException {
  checkCallable();
  try {
    RepositoryState state=repo.getRepositoryState();
    final boolean merging=state.equals(RepositoryState.MERGING) || state.equals(RepositoryState.MERGING_RESOLVED);
    final boolean cherryPicking=state.equals(RepositoryState.CHERRY_PICKING) || state.equals(RepositoryState.CHERRY_PICKING_RESOLVED);
    final boolean reverting=state.equals(RepositoryState.REVERTING) || state.equals(RepositoryState.REVERTING_RESOLVED);
    final ObjectId commitId=resolveRefToCommitId();
    if (ref != null && commitId == null) {
      throw new JGitInternalException("String_Node_Str" + ref + "String_Node_Str");
    }
    final ObjectId commitTree;
    if (commitId != null)     commitTree=parseCommit(commitId).getTree();
 else     commitTree=null;
    if (!filepaths.isEmpty()) {
      resetIndexForPaths(commitTree);
      setCallable(false);
      return repo.getRef(Constants.HEAD);
    }
    final Ref result;
    if (commitId != null) {
      final RefUpdate ru=repo.updateRef(Constants.HEAD);
      ru.setNewObjectId(commitId);
      String refName=Repository.shortenRefName(getRefOrHEAD());
      String message=refName + "String_Node_Str" + Constants.HEAD;
      ru.setRefLogMessage(message,false);
      if (ru.forceUpdate() == RefUpdate.Result.LOCK_FAILURE)       throw new JGitInternalException(MessageFormat.format(JGitText.get().cannotLock,ru.getName()));
      ObjectId origHead=ru.getOldObjectId();
      if (origHead != null)       repo.writeOrigHead(origHead);
      result=ru.getRef();
    }
 else {
      result=repo.getRef(Constants.HEAD);
    }
    if (mode == null)     mode=ResetType.MIXED;
switch (mode) {
case HARD:
      checkoutIndex(commitTree);
    break;
case MIXED:
  resetIndex(commitTree);
break;
case SOFT:
break;
case KEEP:
case MERGE:
throw new UnsupportedOperationException();
}
if (mode != ResetType.SOFT) {
if (merging) resetMerge();
 else if (cherryPicking) resetCherryPick();
 else if (reverting) resetRevert();
 else if (repo.readSquashCommitMsg() != null) repo.writeSquashCommitMsg(null);
}
setCallable(false);
return result;
}
 catch (IOException e) {
throw new JGitInternalException(JGitText.get().exceptionCaughtDuringExecutionOfResetCommand,e);
}
}

Fixed version (ground truth):
/** 
 * Executes the   {@code Reset} command. Each instance of this class shouldonly be used for one invocation of the command. Don't call this method twice on an instance.
 * @return the Ref after reset
 * @throws GitAPIException
 */
public Ref call() throws GitAPIException, CheckoutConflictException {
  checkCallable();
  try {
    RepositoryState state=repo.getRepositoryState();
    final boolean merging=state.equals(RepositoryState.MERGING) || state.equals(RepositoryState.MERGING_RESOLVED);
    final boolean cherryPicking=state.equals(RepositoryState.CHERRY_PICKING) || state.equals(RepositoryState.CHERRY_PICKING_RESOLVED);
    final boolean reverting=state.equals(RepositoryState.REVERTING) || state.equals(RepositoryState.REVERTING_RESOLVED);
    final ObjectId commitId=resolveRefToCommitId();
    if (ref != null && commitId == null) {
      throw new JGitInternalException("String_Node_Str" + ref + "String_Node_Str");
    }
    final ObjectId commitTree;
    if (commitId != null)     commitTree=parseCommit(commitId).getTree();
 else     commitTree=null;
    if (!filepaths.isEmpty()) {
      resetIndexForPaths(commitTree);
      setCallable(false);
      return repo.getRef(Constants.HEAD);
    }
    final Ref result;
    if (commitId != null) {
      final RefUpdate ru=repo.updateRef(Constants.HEAD);
      ru.setNewObjectId(commitId);
      String refName=Repository.shortenRefName(getRefOrHEAD());
      String message=refName + "String_Node_Str" + Constants.HEAD;
      ru.setRefLogMessage(message,false);
      if (ru.forceUpdate() == RefUpdate.Result.LOCK_FAILURE)       throw new JGitInternalException(MessageFormat.format(JGitText.get().cannotLock,ru.getName()));
      ObjectId origHead=ru.getOldObjectId();
      if (origHead != null)       repo.writeOrigHead(origHead);
      result=ru.getRef();
    }
 else {
      result=repo.getRef(Constants.HEAD);
    }
    if (mode == null)     mode=ResetType.MIXED;
switch (mode) {
case HARD:
      checkoutIndex(commitTree);
    break;
case MIXED:
  resetIndex(commitTree);
break;
case SOFT:
break;
case KEEP:
case MERGE:
throw new UnsupportedOperationException();
}
if (mode != ResetType.SOFT) {
if (merging) resetMerge();
 else if (cherryPicking) resetCherryPick();
 else if (reverting) resetRevert();
 else if (repo.readSquashCommitMsg() != null) repo.writeSquashCommitMsg(null);
}
setCallable(false);
return result;
}
 catch (IOException e) {
throw new JGitInternalException(MessageFormat.format(JGitText.get().exceptionCaughtDuringExecutionOfResetCommand,e.getMessage()),e);
}
}