public Phenotype<G, C> nullifyFitness() {
		return _fitness != null ? of(_genotype, _generation) : this;
	}
Return a phenotype, where the fitness is set to {@code null}. If
{@code this} phenotype isn't evaluated, {@code this} instance is returned.

@since 6.0

@return a phenotype, where the fitness is set to {@code null}
jenetics/src/main/java/io/jenetics/Phenotype.java