Nullability warning is missing on the lock statement

Version Used: 17.13.0 Preview 2.1

There is no nullability warning for lock (null) { } or lock (maybeNullExpr) { }, even though a null at runtime throws ArgumentNullException.

Expected

A nullability warning such as:

• CS8604 - Possible null reference argument for parameter.

  • More literal, similar to how await or foreach simply reflect the warning you'd get if you had manually called GetAwaiter()/GetEnumerator().

• CS8602 - Dereference of a possibly null reference.

  • A step back, if calling expr in lock (expr) a "parameter" is leaking too much information about how lock is being lowered.

Or, one in the same vein as "CS8597 Thrown value may be null."