How should I use 0x21 frames when there are zero hops?

ZigBee mesh network, API2, testing nodes with XCTU.
I expect the network to get large so I am using many-to-one addressing with source routing in the program that I am writing. In order to test the nodes I am using XCTU. When I use the frame generator to write a frame with zero hops it complains if I don’t put 00 00 in the addresses field. When I do this and later open the frame for editing the frame generator says that the frame is not valid. Do I need to skip the 0x21 frame if the path is direct?

Yes you should.