### What it does
This lint checks for invalid usages of `ptr::null`.

### Why is this bad?
This causes undefined behavior.

### Example
```
// Undefined behavior
unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
```

Use instead:
```
unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
```