映射错误.从HasKey映射中删除了LocationId.

The mapping was wrong. Removed LocationId from the HasKey mapping.

好像LINQ将某个属性视为键的一部分，它将假定它是不可为空的，而该属性是否为可为null(int?)

Seems like if LINQ sees a property as part of a key it will assume it is non-nullable, does not matter if the property is nullable (int?)