code: @Nullable
    public String getResponseBodyAsString (@Nonnull final Charset aCharset)
    {
      return m_aResponseBody == null ? null : new String (m_aResponseBody, aCharset);
    }
docs: Get the response body as a string in the provided charset.
  
  @param aCharset
  The charset to use. May not be <code>null</code>.
  @return <code>null</code> if no response body is present.