az account set error

[JasonRShaver]

When entering 'az account set' it shows error info instead of usage info:

(env35) jasonsha@JasonShaMBP: ~/temp $ az account set
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 170, in _run_module_as_main
"main", mod_spec)
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/Users/jasonsha/code/azure-cli/src/azure/cli/main.py", line 24, in
sys.exit(azure.cli.main.main(args))
File "/Users/jasonsha/code/azure-cli/src/azure/cli/main.py", line 39, in main
cmd_result = app.execute(args)
File "/Users/jasonsha/code/azure-cli/src/azure/cli/application.py", line 81, in execute
result = args.func(converted_params)
File "/Users/jasonsha/code/azure-cli/src/command_modules/azure-cli-profile/azure/cli/command_modules/profile/account.py", line 48, in set_active_subscription
profile.set_active_subscription(subscription_id)
File "/Users/jasonsha/code/azure-cli/src/azure/cli/_profile.py", line 138, in set_active_subscription
subscription_id_or_name = subscription_id_or_name.lower()
AttributeError: 'NoneType' object has no attribute 'lower'

[mayurid]

@yugangw-msft: Yugang can you take a look? Most places we don't see a call stack
@johanste as FYI