code: def gather(cls, comm, in_array, out_array, root=0, stream=None):
      # out_array is a list of sparse matrices
      if comm.rank == root:
          for peer in range(comm._n_devices):
              res = _make_sparse_empty(
                  in_array.dtype, _get_sparse_type(in_array)
              )
              if peer != root:
                  cls.recv(comm, res, peer, stream)
              else:
                  cls._assign_arrays(
                      res,
                      cls._get_internal_arrays(in_array),
                      in_array.shape,
                  )
              out_array.append(res)
      else:
          cls.send(comm, in_array, root, stream)
  
imports: import numpy
  import warnings
  import cupy
  from cupy.cuda import nccl
  from cupyx.distributed import _store
  from cupyx.distributed._comm import _Backend
  from cupyx.scipy import sparse
label_desc: Use image node_id 16 for calling the _SparseNCCLCommunicator obj's underlying member method code with example usage: obj.gather(cls, comm, in_array, out_array, root, stream) without return types