code: func (s *Cache) Delete(key string) error {
  	lckStatus := s.removeExpired()
  
  	_, err := s.unsafeGet(key)
  	if err != nil {
  		return err
  	}
  
  	if lckStatus == raiqub.ReadLocked {
  		s.RUnlock()
  		s.Lock()
  	}
  	defer s.Unlock()
  
  	delete(s.values, key)
  	return nil
  }
docs: // Delete deletes the specified key:value.
  //
  // Errors:
  // InvalidKeyError when requested key could not be found.