code: function (field) {
              if (field === undefined) {
                  this.field = [];
              } else {
                  this.fields[field] = undefined;
              }
              this.time = undefined;
              this.fieldsComputed = false;
          }
docs: Sets all the calendar field values or specified field and the time value
  (millisecond offset from the Epoch) of this Calendar undefined.
  This means that isSet() will return false for all the calendar fields,
  and the date and time calculations will treat the fields as if they had never been set.
  @param [field] the calendar field to be cleared.