code: @Nullable
    public static IHCNode markdownOnDemand (@Nullable final String sMD)
    {
      return StringHelper.hasText (sMD) ? markdown (sMD) : null;
    }
docs: Same as {@link #markdown(String)} but returning <code>null</code> if the
  passed string is <code>null</code> or empty.
  
  @param sMD
  The Markdown source to be invoked. May be <code>null</code>.
  @return <code>null</code> if the parameter is <code>null</code> or empty.
  @see #markdown(String)