code: def merge_user_commits(cls, commits):
          
          user = None
          for commit in commits:
              if not user:
                  user = commit
              else:
                  if commit.committer_time > user.committer_time:
                      commit.line_count += user.line_count
                      user = commit
                  else:
                      user.line_count += commit.line_count
          return user
docs: Merge all the commits for the user.
  
          Aggregate line counts, and use the most recent commit (by date/time)
          as the representative commit for the user.