code: public static CharacterGene of(final CharSeq validCharacters) {
  		return new CharacterGene(
  			validCharacters,
  			RandomRegistry.getRandom().nextInt(validCharacters.length())
  		);
  	}
docs: Create a new CharacterGene with a randomly chosen character from the
  set of valid characters.
  
  @param validCharacters the valid characters for this gene.
  @return a new valid, <em>random</em> gene,
  @throws NullPointerException if the {@code validCharacters} are
  {@code null}.