code: func validateMergeKeyInLists(mergeKey string, lists ...[]interface{}) error {
  	for _, list := range lists {
  		for _, item := range list {
  			m, ok := item.(map[string]interface{})
  			if !ok {
  				return mergepatch.ErrBadArgType(m, item)
  			}
  			if _, ok = m[mergeKey]; !ok {
  				return mergepatch.ErrNoMergeKey(m, mergeKey)
  			}
  		}
  	}
  	return nil
  }
docs: // validateMergeKeyInLists checks if each map in the list has the mentryerge key.