better error message when instance is missing

__init__.py

@@ -93,7 +93,7 @@ def run(group, arglist):
             args.setdefault('action', 'gui')
             print('do you mean:\n   %s %s %s %s %s' %
                   (group, args.get('action', ''), args.get('ins', ''), args.get('service', ''), ' '.join(extra)))
-        else:            
+        else:
             try:
                 serv.action(args['action'], *serv.treat_args(args, extra + arglist))
             except AttributeError:

base.py

@@ -281,6 +281,8 @@ class ServiceManager:
         if ins not in self.env:
             self.get_info()
         gr = self.group.upper()
+        if not ins:
+            raise UsageError('need instance')
         env = self.env[ins]
         return env.get('%s_ROOT' % gr, ''), env