[tune] Allow None values in TBX logger (#12262)

python/ray/tune/logger.py

@@ -199,8 +199,8 @@ class TBXLogger(Logger):
         {"a": {"b": 1, "c": 2}} -> {"a/b": 1, "a/c": 2}
     """
 
-    # NoneType is not supported on the last TBX release yet.
-    VALID_HPARAMS = (str, bool, np.bool8, int, np.integer, float, list)
+    VALID_HPARAMS = (str, bool, np.bool8, int, np.integer, float, list,
+                     type(None))
 
     def _init(self):
         try:

python/ray/tune/tests/test_logger.py

@@ -147,7 +147,8 @@ class LoggerSuite(unittest.TestCase):
                 }
             },
             "d": np.int64(1),
-            "e": np.bool8(True)
+            "e": np.bool8(True),
+            "f": None,
         }
         t = Trial(
             evaluated_params=config, trial_id="tbx", logdir=self.test_dir)