geodist command float casting bug

[fengshenyuan]

I got an exception when test with geodist command.
The traceback of this exception is here:

Traceback (most recent call last):
      File "/home/diyidan_backstage/api_pre/master/user.py", line 628, in get_user_and_me_distance_for_user_profile
        user_and_me_distance = REDIS_CLIENT_GEO.geodist(name=name, place1=current_user_id, place2=check_user_id, unit='m')
      File "/usr/lib/python2.7/site-packages/redis/client.py", line 2135, in geodist
        return self.execute_command('GEODIST', *pieces)
      File "/usr/lib/python2.7/site-packages/redis/client.py", line 668, in execute_command
        return self.parse_response(connection, command_name, **options)
      File "/usr/lib/python2.7/site-packages/redis/client.py", line 682, in parse_response
        return self.response_callbacks[command_name](response, **options)
    TypeError: float() argument must be a string or a number

I checked the current implement of GEODIST command in redis-py.
In source file client.py, line 373, I find code:

  string_keys_to_dict(
            'INCRBYFLOAT HINCRBYFLOAT GEODIST',
            float
        ),

Then I checked official document of GEODIST. It says:

If one or both the members are missing, the command returns NULL.

I think we can get the bug now: the RESPONSE_CALLBACKS setting for command GEODIST cannot just be float.
And I found test items of command GEODIST in test_commands.py is lack of this situation.
I'll try to fix this bug with a pull request.