value_t normalize_value(const std::string& s) const {
				std::map<std::string, value_t>::const_iterator it = values.find(s);
				if(it == values.end()) {
					return value_default;
				}
				else {
					return it->second;
				}
			}
	// Handle request for the pair.
	// Throws an exception if pair is not found.
	std::string handle_request_for_pair(
		const msg_request_by_key & what )
	{
		auto r = m_values.find( what.m_key );
		if( r == m_values.end() )
			throw key_not_found_exception( "key is not found in the storage: " +
					what.m_key );

		return r->second;
	}