code: @Nonnull
    @OverrideOnDemand
    protected <T> T executeRequest (@Nonnull final HttpRequestBase aRequest,
                                    @Nonnull final ResponseHandler <T> aHandler) throws IOException
    {
      // Contextual attributes set the local context level will take
      // precedence over those set at the client level.
      final HttpContext aContext = HttpClientHelper.createHttpContext (m_aProxy, m_aProxyCredentials);
      return m_aHttpClientMgr.execute (aRequest, aContext, aHandler);
    }
docs: The main execution routine. Overwrite this method to add additional
  properties to the call.
  
  @param aRequest
  The request to be executed. Never <code>null</code>.
  @param aHandler
  The response handler to be used. May not be <code>null</code>.
  @return The return value of the response handler. Never <code>null</code>.
  @throws IOException
  On HTTP error
  @param <T>
  Response type