docs: def get_process_runtime_cache(self, key, pid=None):
          '''
          get_process_runtime_cache(self, key, pid=None)
  
          Get a pre-defined run time parameter value
  
          :Parameters:
          * *key* (`string`) -- Identifier of the runtime cache
          * *pid* (`string`) -- Identifier of an existing process
  
          '''
          value = None
          pid = self._get_pid(pid)
          value = self._call_rest_api('get', '/processes/'+pid+'/cache?key=%s'%key, error='Failed to fetch process runtime cache')
          return value