基本上，我有一个垂直的UIStackView，其中填充了容器视图。 我在容器视图上看到空属性（？）
"NSLayoutConstraint:0x600000c3ed50 UICollectionView:0x7f954c871000.leading == UIView:0x7f954c5a5330.(null)"
此约束试图与之进行比较？此地址（0x7f954c5a5330）中还有其他不为空的属性（.trailing，.left，.width等），我该如何解决？
我猜想只有在隐藏容器视图时约束才会打破，但是我不确定。
完整输出如下：
"<NSLayoutConstraint:0x600000c3ed50 UICollectionView:0x7f954c871000.leading == UIView:0x7f954c5a5330.(null)>",
"<NSLayoutConstraint:0x600000c3edf0 UIView:0x7f954c5a5330.trailing == UICollectionView:0x7f954c871000.trailing>",
"<NSLayoutConstraint:0x600000c3b7a0 UIView:0x7f954c5a5330.width == 0>",
"<NSLayoutConstraint:0x600000c3f0c0 UILayoutGuide:0x6000016d9960.left == UIView:0x7f954c5a5330.left + 20>"
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x600000c3ed50 UICollectionView:0x7f954c871000.leading == UIView:0x7f954c5a5330.(null)>