code: public ModifyCallResponse transferCall(String uuid, String nccoUrl) throws IOException, NexmoClientException {
          return this.modifyCall(CallModifier.transferCall(uuid, nccoUrl));
      }
docs: Transfer a call to a different NCCO endpoint.
  
  @param uuid    The UUID of the call, obtained from the object returned by {@link #createCall(Call)}. This value can
  be obtained with {@link CallEvent#getUuid()}
  @param nccoUrl The URL of the NCCO endpoint the call should be transferred to
  
  @return A ModifyCallResponse object, representing the response from the Nexmo Voice API.
  
  @throws IOException          if a network error occurred contacting the Nexmo Voice API.
  @throws NexmoClientException if there was a problem with the Nexmo request or response objects.