docs: 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);
      }