code: func keysUnion(maps ...map[string]interface{}) []string {
  	keys := map[string]interface{}{}
  	for _, m := range maps {
  		for k := range m {
  			keys[k] = nil
  		}
  	}
  	result := []string{}
  	for key := range keys {
  		result = append(result, key)
  	}
  	return result
  }
docs: // keysUnion returns a slice containing the union of the keys present in the arguments