Query headOrDefault and exactlyOneOrDefault with a struct/tuple

What should the following syntax do:

```fsharp
open System
open System.Linq

let myQueryable = [|(1,1); (2,2)|].AsQueryable()
let a, b =
query {
for x in myQueryable do
where(x = (3,3))
headOrDefault
}
```

Currently it compiles, but produces a runtime System.NullReferenceException. A thing that we shouldn't have in FSharp, right?

Edit: The reason is...well, read the replies.