anchor.diff:     * If [indent] is `null`, the output is encoded as a single line.
      *
      * The JSON encoder handles numbers, strings, booleans, null, lists and
  -   * maps directly.
  +   * maps with string keys directly.
      *
      * Any other object is attempted converted by [toEncodable] to an
      * object that is of one of the convertible types.
  
positive.code:    * If [toEncodable] is omitted, it defaults to calling `.toJson()` on
     * the object.
     */
    const JsonEncoder([toEncodable(nonSerializable)])
        : this.indent = null,
          this._toEncodable = toEncodable;
  
  
negative.code:    * Creates a JSON encoder.
     *
     * The JSON encoder handles numbers, strings, booleans, null, lists and
     * maps with string keys directly.
     *
     * Any other object is attempted converted by [toEncodable] to an
     * object that is of one of the convertible types.
  