code: protected final void checkNotNull(final ConversionStringency stringency,
                                        final Logger logger) {
          if (stringency == null) {
              throw new NullPointerException("stringency must not be null");
          }
          if (logger == null) {
              throw new NullPointerException("logger must not be null");
          }
      }
docs: Check the specified conversion stringency and logger are not null.
  
  @param stringency conversion stringency, must not be null
  @param logger logger, must not be null
  @throws NullPointerException if either conversion stringency or logger are null