MAVProxy MPState Error

The following command gives me this error
(trying to connect to Arducopter onboard)

`mavproxy.py --master=udp:127.0.0.1:14650`

**Result**:

Connect udp:127.0.0.1:14650 source_system=255
Traceback (most recent call last):
File "/usr/local/bin/mavproxy.py", line 1084, in
load_module(m, quiet=True)
File "/usr/local/bin/mavproxy.py", line 281, in load_module
module = m.init(mpstate)
File "/home/pi/.local/lib/python2.7/site-packages/MAVProxy/modules/mavproxy_param.py", line 433, in init
return ParamModule(mpstate, **kwargs)
File "/home/pi/.local/lib/python2.7/site-packages/MAVProxy/modules/mavproxy_param.py", line 363, in __init__
self.check_new_target_system()
File "/home/pi/.local/lib/python2.7/site-packages/MAVProxy/modules/mavproxy_param.py", line 410, in check_new_target_system
self.add_new_target_system(sysid)
File "/home/pi/.local/lib/python2.7/site-packages/MAVProxy/modules/mavproxy_param.py", line 383, in add_new_target_system
if not sysid in self.mpstate.mav_param_by_sysid:
AttributeError: 'MPState' object has no attribute 'mav_param_by_sysid'

**Current Development Tools**:

I currently am using Python 2.7.13, and just got mavproxy today. I'm working with a Raspberry Pi as well. Also, I've gone through the installation steps as listed in https://ardupilot.github.io/MAVProxy/html/getting_started/download_and_installation.html.

Start with the failing command and traceback, then inspect MAVProxy/modules/mavproxy_param.py around ParamModule, check_new_target_system, and add_new_target_system. Reproduce the error with the documented installation and Python 2.7 environment; done means the command no longer raises the reported MPState AttributeError during connection.

Written by the indexing model from the issue text.