docs: @Nonnull
    protected MockHttpServletResponse getMockHttpServletResponse (@Nonnull final ServletResponse aResponse)
    {
      if (aResponse instanceof MockHttpServletResponse)
        return (MockHttpServletResponse) aResponse;
      if (aResponse instanceof HttpServletResponseWrapper)
        return getMockHttpServletResponse (((HttpServletResponseWrapper) aResponse).getResponse ());
  
      throw new IllegalArgumentException ("MockRequestDispatcher requires MockHttpServletResponse");
    }