Set a clear default value for validate_only

Be explicit with the `validate_only`. The code was previously sending a
`False` so this just makes it more explicit and reduces ambiguity.

kafka/admin/kafka.py

@@ -299,12 +299,13 @@ def _convert_new_topic_request(new_topic):
             ]
         )
 
-    def create_topics(self, new_topics, timeout_ms=None, validate_only=None):
+    def create_topics(self, new_topics, timeout_ms=None, validate_only=False):
         """Create new topics in the cluster.
 
         :param new_topics: Array of NewTopic objects
         :param timeout_ms: Milliseconds to wait for new topics to be created before broker returns
-        :param validate_only: If True, don't actually create new topics.  Not supported by all versions.
+        :param validate_only: If True, don't actually create new topics.
+            Not supported by all versions. Default: False
         :return: Appropriate version of CreateTopicResponse class
         """
         version = self._matching_api_version(CreateTopicsRequest)
@@ -319,7 +320,6 @@ def create_topics(self, new_topics, timeout_ms=None, validate_only=None):
                 timeout = timeout_ms
             )
         elif version <= 2:
-            validate_only = validate_only or False
             request = CreateTopicsRequest[version](
                 create_topic_requests = [self._convert_new_topic_request(new_topic) for new_topic in new_topics],
                 timeout = timeout_ms,
@@ -445,17 +445,17 @@ def _convert_create_partitions_request(topic_name, new_partitions):
             )
         )
 
-    def create_partitions(self, topic_partitions, timeout_ms=None, validate_only=None):
+    def create_partitions(self, topic_partitions, timeout_ms=None, validate_only=False):
         """Create additional partitions for an existing topic.
 
         :param topic_partitions: A map of topic name strings to NewPartition objects
         :param timeout_ms: Milliseconds to wait for new partitions to be created before broker returns
         :param validate_only: If True, don't actually create new partitions.
+            Default: False
         :return: Appropriate version of CreatePartitionsResponse class
         """
         version = self._matching_api_version(CreatePartitionsRequest)
         timeout_ms = self._validate_timeout(timeout_ms)
-        validate_only = validate_only or False
         if version == 0:
             request = CreatePartitionsRequest[version](
                 topic_partitions = [self._convert_create_partitions_request(topic_name, new_partitions) for topic_name, new_partitions in topic_partitions.items()],