code: private static void checkPreconditions(final Collection<Integer> requriedLengths) {
          if( requriedLengths == null ) {
              throw new NullPointerException("requriedLengths should not be null");
          } else if( requriedLengths.isEmpty()) {
              throw new IllegalArgumentException("requriedLengths should not be empty");
          }
      }
docs: Checks the preconditions for creating a new {@link LengthExact} processor.
  
  @param requriedLengths
  one or more required lengths
  @throws NullPointerException
  if requiredLengths is null
  @throws IllegalArgumentException
  if requiredLengths is empty