Minor request to improve user feedback when not using Bitmask as intended:

➜  bitmask-0.10.0 ./bitmask keys export help
ERROR: 'NoneType' object has no attribute 'endswith'
➜  bitmask-0.10.0 ./bitmask keys export --help
usage: bitmask keys export [-h] [-u USERID] [--private] [--fetch] address

Bitmask export key

positional arguments:
  address               email address of the key

optional arguments:
  -h, --help            show this help message and exit
  -u USERID, --userid USERID
                        Select the userid of the keyring
  --private             Use private keys (by default uses public)
  --fetch               Try to fetch remotely the key if it is not in the
                        local storage

Some feedback like 'one argument too much' or 'did you mean --help?' would be nice.