[PyTorch] Fix backward compatibility for checkpoint API (#748)

* Args can be None

Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix other arg types

Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

---------

Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

transformer_engine/pytorch/distributed.py

@@ -516,12 +516,6 @@ def checkpoint(
     kwargs : dict
             dictionary of string keys for keyword arguments to :attr:`function`.
     """
-    only_tensor_args = True
-    for arg in args:
-        if not isinstance(arg, torch.Tensor):
-            only_tensor_args = False
-            break
-
     # Pop out te.distributed.checkpoint() arguments
     global _USE_REENTRANT_ACTIVATION_RECOMPUTE
     _USE_REENTRANT_ACTIVATION_RECOMPUTE = kwargs.pop("use_reentrant", True)
@@ -530,23 +524,14 @@ def checkpoint(
     get_rng_state_tracker = kwargs.pop("get_rng_state_tracker", None)
 
     # Ensure backward compatibility.
-    if not only_tensor_args:
+    if (len(args) > 3 and isinstance(args[0], bool) and callable(args[1])
+        and isinstance(args[2], None | dist_group_type)):
         warnings.warn(
             "Passing non-tensor non-keyword arguments is deprecated and support will be removed in "
             "future releases of TransformerEngine. `distribute_saved_activations`, `tp_group`, and "
             "`get_rng_state_tracker` must be passed as keyword arguments to `checkpoint`.",
             DeprecationWarning, stacklevel=2,
         )
-        assert len(args) > 3, "Incorrect number of arguments for deprecated `checkpoint` API."
-        assert (
-            isinstance(args[0], bool) and callable(args[1])
-            and isinstance(args[2], None | dist_group_type)
-        ), "Incorrect arguments for deprecated `checkpoint` API."
-        for arg in args[3:]:
-            assert (
-                isinstance(arg, None | torch.Tensor)
-            ), f"Expected tensor argument, found {type(arg)}."
-
         distribute_saved_activations, get_rng_state_tracker, tp_group = args[:3] # pylint: disable=unbalanced-tuple-unpacking
         args = args[3:]