Null cast

[r-barnes]

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.

[d4l3k]

It's a fair point though, looks like this is upstream code from RCCL https://github.com/ROCm/rccl/blob/4acd0f64eabad20bb3af210ac0e986415970f1da/src/device/all_gather.h#L73

I'm not sure how much we want to diverge from upstream