code: private static void checkPreconditions(List<String> requiredSubStrings) {
  		if( requiredSubStrings == null ) {
  			throw new NullPointerException("requiredSubStrings List should not be null");
  		} else if( requiredSubStrings.isEmpty() ) {
  			throw new IllegalArgumentException("requiredSubStrings List should not be empty");
  		}
  	}
docs: Checks the preconditions for creating a new RequireSubStr processor with a List of Strings.
  
  @param requiredSubStrings
  the required substrings
  @throws NullPointerException
  if requiredSubStrings or one of its elements is null
  @throws IllegalArgumentException
  if requiredSubStrings is empty