I think we should be nice and offer a couple of overloads here:

  public CommitCommand setAuthor(String name, String email)
  public CommitCommand setAuthor(String name, String email, Date when)
  public CommitCommand setAuthor(String name, String email, Date when, TimeZone tz)

Or

  public CommitCommand setAuthorName(String name)
  public CommitCommand setAuthorEmail(String email)
  public CommitCommand setAuthorDate(Date when)

so applications can more easily just assign the author.  Having to make a PersonIdent can be sort of annoying.