guard against None in pytorch get_xla_supported_devices (#9572)

Co-authored-by: Chris Chow <cchow@nianticlabs.com>
Co-authored-by: thomas chaton <thomas@grid.ai>

CHANGELOG.md

@@ -469,6 +469,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `BasePredictionWriter` not returning the batch_indices in a non-distributed setting ([#9432](https://github.com/PyTorchLightning/pytorch-lightning/pull/9432))
 
 
+- Fixed an error when running on in XLA environments with no TPU attached ([#9572](https://github.com/PyTorchLightning/pytorch-lightning/pull/9572))
+
+
 - Fixed check on torchmetrics logged whose `compute()` output is a multielement tensor ([#9582](https://github.com/PyTorchLightning/pytorch-lightning/pull/9582))
 
 

pytorch_lightning/utilities/xla_device.py

@@ -70,9 +70,7 @@ class XLADeviceUtils:
         # we would have to use `torch_xla.distributed.xla_dist` for
         # multiple VMs and TPU_CONFIG won't be available, running
         # `xm.get_xla_supported_devices("TPU")` won't be possible.
-        if xm.xrt_world_size() > 1:
-            return True
-        return len(xm.get_xla_supported_devices("TPU")) > 0
+        return (xm.xrt_world_size() > 1) or bool(xm.get_xla_supported_devices("TPU"))
 
     @staticmethod
     def xla_available() -> bool: