anchor.diff:        'GitReference: $reference  $sha';
   }
   
  -class BranchReference extends GitReference {
  +class BranchReference extends CommitReference {
     static const _localBranchPrefix = r'refs/heads/';
   
     final String branchName;
  
positive.code:     return _shaRegEx.hasMatch(value);
    }
  
    static List<GitReference> parseLsRemoteOutput(String input) {
      assert(input != null);
      final lines = Util.splitLines(input);
  
  
negative.code: /**
   * Represents the output from `git ls-remote`
   */
  class CommitReference {
    final String sha;
    final String reference;
  
    CommitReference(this.sha, this.reference) {
      assert(Git.isValidSha(sha));
  
      assert(reference != null);
  