fix: use explicit is not None check for row_range in client

Updates the row_range check in both async and sync clients to use an explicit `is not None` check rather than truthiness evaluation.

TAG=agy
CONV=6cea44b5-6adb-45c6-b8c8-58b37f95584c

Author: anvitTawar

packages/google-cloud-bigtable/google/cloud/bigtable/data/_async/client.py

@@ -1447,7 +1447,7 @@ async def execute_rpc():
                 results = await self.client._gapic_client.sample_row_keys(
                     request=SampleRowKeysRequest(
                         app_profile_id=self.app_profile_id,
-                        row_range=row_range._to_pb() if row_range else None,
+                        row_range=row_range._to_pb() if row_range is not None else None,
                         **self._request_path
                     ),
                     timeout=next(attempt_timeout_gen),

packages/google-cloud-bigtable/google/cloud/bigtable/data/_sync_autogen/client.py

@@ -1191,7 +1191,7 @@ def execute_rpc():
                 results = self.client._gapic_client.sample_row_keys(
                     request=SampleRowKeysRequest(
                         app_profile_id=self.app_profile_id,
-                        row_range=row_range._to_pb() if row_range else None,
+                        row_range=row_range._to_pb() if row_range is not None else None,
                         **self._request_path,
                     ),
                     timeout=next(attempt_timeout_gen),