Null cast

This looks bad:

In file included from buck-out/v2/gen/fbcode/6db5ac18a0c7a447/comms/rcclx/__generate_collectives__/out/develop/src/device/all_gather_sum_i8.hip:2:
buck-out/v2/gen/fbcode/comms/rcclx/__rccl_objects__/81d40f005b45f43a/buck-headers/all_gather.h:71:135: warning: implicit conversion of NULL constant to 'bool' [-Wnull-conversion]
   70 |       Primitives<T, RedOp, FanSymmetric<1>, 0, Proto, 0, isNetOffload> prims
      |                                                                        ~~~~~
   71 |         (tid, workNthreads, &ring->prev, &ring->next, inputBuf, outputBuf, work->redOpArg, 0, work->connIndex, work->connIndex, work, NULL, isNetOffload ? NCCL_MAX_NET_SIZE : 0);
      |                                                                                                                                       ^~~~
      |                                                                                                                                       false

especially with that actual boolean right next door to the NULL.

Enabling -Wnull-conversion in your project and using the now-standard nullptr would prevent these issues.

Start at the generated all_gather.h around line 71 and trace which source produces the NULL argument passed beside the boolean isNetOffload. Enable -Wnull-conversion to reproduce the warning, then replace the relevant null pointer constant with nullptr and verify that the warning is gone.