anchor.diff:            "string.");
       }
   
  -    // Ensure that it's a valid URL.
  -    Uri.parse(description["url"]);
  +    _validateUrl(description["url"]);
   
       var ref = description["ref"];
       if (ref != null && ref is! String) {
  
positive.code:       "ref": description["ref"] ?? "HEAD",
        "resolved-ref": description["resolved-ref"]
      });
    }
  
    /// If [description] has a resolved ref, print it out in short-form.
  
negative.code:           "string.");
      }
  
      _validateUrl(description["url"]);
  
      var ref = description["ref"];
      if (ref != null && ref is! String) {
  