Fix test_fetch_identifier for missing optional build_time

If the running test trace server doesn't provide build_time which is
optional then the test case fails. This commit fixes it.

Signed-off-by: Bernd Hufmann <[email protected]>

Author: bhufmann

test_tsp.py

@@ -585,7 +585,9 @@ def test_fetch_identifier(self):
         assert response.status_code == 200
         assert response.model
         assert response.model.server_version
-        assert response.model.build_time
+        # optional field build_time
+        if response.model.build_time is not None:
+            assert response.model.build_time
         assert response.model.os_name
         assert response.model.os_arch
         assert response.model.os_version