Invalid throw expression typeDRT-W1643

The analyzer produces this diagnostic when the type of the expression in a throw expression isn't assignable to Object. It isn't valid to throw null, so it isn't valid to use an expression that might evaluate to null.

Example

The following code produces this diagnostic because s might be null:

void f(String? s) {
  throw s;
}

Common fixes

Add an explicit null-check to the expression:

void f(String? s) {
  throw s!;
}