code: public static Codec<Double, DoubleGene> ofScalar(final DoubleRange domain) {
  		requireNonNull(domain);
  
  		return Codec.of(
  			Genotype.of(DoubleChromosome.of(domain)),
  			gt -> gt.getGene().getAllele()
  		);
  	}
docs: Return a scalar {@code Codec} for the given range.
  
  @param domain the domain of the returned {@code Codec}
  @return a new scalar {@code Codec} with the given domain.
  @throws NullPointerException if the given {@code domain} is {@code null}