/// <summary>
/// 访问 <see cref="OuterJoinedExpression"/>。
/// </summary>
/// <param name="outer">要访问的表达式。</param>
/// <returns></returns>
protected virtual Expression VisitOuterJoined(OuterJoinedExpression outer)
{
var test = Visit(outer.Test);
var expression = Visit(outer.Expression);
return(outer.Update(test, expression));
}
