Throw a null type exception when `database` is null (i.e. can't be found in the server)

[AdityaNPL]

On line 119:

AgDatabaseMove/src/SmoFacade/Server.cs

Lines 115 to 121 in 683f409

	public Database Database(string dbName)
	{
	// The database collection is cached and not invalidated on database creation (with a second server object).
	_server.Databases.Refresh();
	var database = _server.Databases[dbName];
	return database == null ? null : new Database(database, this);
	}