code: public static DateTimeField getInstance(DateTimeField field) {
          if (field == null) {
              return null;
          }
          if (field instanceof LenientDateTimeField) {
              field = ((LenientDateTimeField)field).getWrappedField();
          }
          if (!field.isLenient()) {
              return field;
          }
          return new StrictDateTimeField(field);
      }
docs: Returns a strict version of the given field. If it is already strict,
  then it is returned as-is. Otherwise, a new StrictDateTimeField is
  returned.