code: func (m NiceMD) Del(key string) NiceMD {
  	k, _ := encodeKeyValue(key, "")
  	delete(m, k)
  	return m
  }
docs: // Del retrieves a single value from the metadata.
  //
  // It works analogously to http.Header.Del, deleting all values if they exist.
  //
  // The function is binary-key safe.