def check_env(self, envar, value):
        '''ensure that variable envar is set to some value, 
           otherwise exit on error.
        
           Parameters
           ==========
           envar: the environment variable name
           value: the setting that shouldn't be None
        '''
        if value is None:
            bot.error('You must export %s to use Discourse' % envar)
            print('https://vsoch.github.io/helpme/helper-discourse')
            sys.exit(1)
ensure that variable envar is set to some value, 
           otherwise exit on error.
        
           Parameters
           ==========
           envar: the environment variable name
           value: the setting that shouldn't be None