code: function Type(model, value, mutator) {
          var _this = _super.call(this, model) /* istanbul ignore next */ || this;
          /**
           * Whether if the attribute can accept `null` as a value.
           */
          _this.isNullable = false;
          _this.value = value;
          _this.mutator = mutator;
          return _this;
      }
docs: Create a new type instance.