code: public static <S> Function<Double, S> boxArgument(
          final DoubleFunction<S> f, final S returnValueForNullArgument)
      {
          return x -> x == null ? returnValueForNullArgument : f.apply(x);
      }
docs: Returns a view on the given <code>DoubleFunction</code> as a
  <code>Function</code> that accepts a <code>Double</code>,
  thus boxing the argument type from <code>double</code> to
  <code>Double</code>
  
  @param <S> The return value type
  @param f The function
  @param returnValueForNullArgument What is <b>returned</b> when the
  argument that is given to the resulting function is <code>null</code>.
  @return The boxed function