minor fixes

ml-agents/mlagents/trainers/learn.py

         name: importlib.import_module(name)
         for finder, name, ispkg in pkgutil.iter_modules(paths)
     }
-    logger.info(f"The following plugins are available {discovered_plugins}")
+    if discovered_plugins:
+        logger.info(f"The following plugins are available {discovered_plugins}")
-    if len(new_initializers) <= 0:
-        return
+    if len(new_initializers) == 0:
+        return []
     elif len(new_initializers) == 1:
         # load the initializer
         logger.info("Registering new initializer")
         return new_trainers
     else:
         raise ValueError(
-            "there should be exactly one initializer passed through plugins option"
+            "There should be exactly one initializer passed through plugins option."
         )
 
 

ml-agents/mlagents/trainers/policy/tf_policy.py

     GaussianDistribution,
     MultiCategoricalDistribution,
 )
-from mlagents.tf_utils.global_values import get_rank
+from mlagents.tf_utils import global_values
 
 
 logger = get_logger(__name__)
         self.grads = None
         self.update_batch: Optional[tf.Operation] = None
         self.trainable_variables: List[tf.Variable] = []
-        self.rank = get_rank()
+        self.rank = global_values.get_rank()
         if create_tf_graph:
             self.create_tf_graph()