docs: @Nonnull
  	public final LToLongFunctionBuilder<T> withHandling(@Nonnull HandlingInstructions<RuntimeException, RuntimeException> handling) {
  		Null.nonNullArg(handling, "handling");
  		if (this.handling != null) {
  			throw new UnsupportedOperationException("Handling is already set for this builder.");
  		}
  		this.handling = handling;
  		return self();
  	}