code: func (db *DB) Delete(key []byte, wo *opt.WriteOptions) error {
  	return db.putRec(keyTypeDel, key, nil, wo)
  }
docs: // Delete deletes the value for the given key. Delete will not returns error if
  // key doesn't exist. Write merge also applies for Delete, see Write.
  //
  // It is safe to modify the contents of the arguments after Delete returns but
  // not before.