As per sec 9.2.3.3 (formal/99-10-07), from_any should throw an InvalidValue exception if the passed Any does not contain a legal value (such as a null string). I'm here by giving a small piece of code which shows that the intended behaviour is not happening:

    string_tc = orb.get_primitive_tc(TCKind.tk_string);
    factory = (DynAnyFactory)orb.resolve_initial_references("DynAnyFactory");

        Any string_any_1 = orb.create_any();
        string_any_1.type(string_tc);
        string_any_1.insert_string(some_string);

        Any string_any_2 = orb.create_any();
        string_any_2.type(string_tc);
        string_any_2.insert_string(null);

        DynAny string_dynany = factory.create_dyn_any(string_any_1);
        string_dynany.from_any(string_any_1);
        string_dynany.from_any(string_any_2);

The first call to from_any will work fine. However the second call should throw InvalidValue exception. It is not happening that way.