Some platforms append trailing whitespace to the output of the 'ss' command.
Caught thanks to toralf...

  https://github.com/torproject/stem/issues/46

Determined the problem by running the following against toralf's output...

  from stem.util.connection import Resolver, get_connections
  from unittest.mock import patch

  with open('ss-nptu.log') as ss_file:
    ss_output = ss_file.read()

  with patch('stem.util.system.call') as call_mock:
    call_mock.return_value = ss_output.split('\n')

    print('parsed %i connections' % len(get_connections(Resolver.SS, process_pid = 2238, process_name = 'tor')))

Before:

  % python3.7 demo.py
  Traceback (most recent call last):
    File "demo.py", line 12, in <module>
      print('parsed %i connections' % len(get_connections(Resolver.SS, process_pid = 2238, process_name = 'tor')))
    File "/home/atagar/Desktop/stem/stem/util/connection.py", line 333, in get_connections
      raise OSError('No results found using: %s' % resolver_command)
  OSError: No results found using: ss -nptu

After:

  % python3.7 demo.py
  parsed 8114 connections