LanguageFeatures/Patterns/object_A01_t05

[alexmarkov]

This test doesn't account for running without sound null safety (in weak mode):

co19/LanguageFeatures/Patterns/object_A01_t05.dart

Lines 31 to 32 in 780034a

	Expect.throws(() {
	var Square(areaAsNull: d1 as double) = Square(2);

From the spec:

If the runtime type of v is not a subtype of the cast type of p then throw a runtime error.

Without sound null safety Null is a bottom type (subtype of all types), so cast pattern should not throw.