code: func (m *MemoryStorer) Get(key string) (value string, err error) {
  	m.mut.RLock()
  	session, ok := m.sessions[key]
  	m.mut.RUnlock()
  	if !ok {
  		return "", errNoSession{}
  	}
  
  	return session.value, nil
  }
docs: // Get returns the value string saved in the session pointed to by the
  // session id key.