Why am I getting "AttributeError: 'NoneType' object has no attribute 'processor'" using client instance of gramlin_python?

I am using Jupyter Notebook to execute gremlin query over Neptune Database and retrieving information from MySQL database and generating gremlin query string, which is being execute by Client module of "gremlin_python library" as follows.

def getConnectionWithNeptuneGraphDB():
    global clientt
    if clientt is not None:
        print('clientt instance is available')
    else:
        print('clientt is not available')
        clientt = client.Client('neptune_db_endpoint', 'g')
    return clientt

#function to Create Person Node
def createPersonNode():
    personsInfo = getPersonInformation(companyIdTouple)
    print(personsInfo)
    personGremQry = queryToCreatePersonNode(personsInfo)
    clientt = getConnectionWithNeptuneGraphDB()
    clientt.submit(personGremQry)
    #print(personsInfo)
    print('Person Node created successfully')

def main():
    #Process to Create Company Node
    createCompanyNode()
    #Process to Create Person Node
    createPersonNode()      
    connection.close()
    clientt.close()

main() function is entry point here, in execution, createCompanyNode() is working fine and getting company in database but while executing createPersonNode(), this is showing following error, even I have tried only executing createPersonNode(), still the same error.

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-558-263240bbee7e> in <module>
----> 1 main()

<ipython-input-557-e622c1b6eefc> in main()
      1 def main():
      2     #createCompanyNode()
----> 3     createPersonNode()
      4     connection.close()
      5     clientt.close()

<ipython-input-550-60763852d6da> in createPersonNode()
     16     personGremQry = queryToCreatePersonNode(personsInfo)
     17     clientt = getConnectionWithNeptuneGraphDB()
---> 18     clientt.submit(personGremQry)
     19     #print(personsInfo)
     20     print('Person Node created successfully')

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/client.py in submit(self, message, bindings, request_options)
    128 
    129     def submit(self, message, bindings=None, request_options=None):
--> 130         return self.submitAsync(message, bindings=bindings, request_options=request_options).result()
    131 
    132     def submitAsync(self, message, bindings=None, request_options=None):

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    423                 raise CancelledError()
    424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
    426 
    427             self._condition.wait(timeout)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
    382     def __get_result(self):
    383         if self._exception:
--> 384             raise self._exception
    385         else:
    386             return self._result

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/connection.py in cb(f)
     64         def cb(f):
     65             try:
---> 66                 f.result()
     67             except Exception as e:
     68                 future.set_exception(e)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    423                 raise CancelledError()
    424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
    426 
    427             self._condition.wait(timeout)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
    382     def __get_result(self):
    383         if self._exception:
--> 384             raise self._exception
    385         else:
    386             return self._result

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/thread.py in run(self)
     54 
     55         try:
---> 56             result = self.fn(*self.args, **self.kwargs)
     57         except BaseException as exc:
     58             self.future.set_exception(exc)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/protocol.py in write(self, request_id, request_message)
     72     def write(self, request_id, request_message):
     73         message = self._message_serializer.serialize_message(
---> 74             request_id, request_message)
     75         self._transport.write(message)
     76 

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/serializer.py in serialize_message(self, request_id, request_message)
    134 
    135     def serialize_message(self, request_id, request_message):
--> 136         processor = request_message.processor
    137         op = request_message.op
    138         args = request_message.args

AttributeError: 'NoneType' object has no attribute 'processor'