TEST(RegexMatchExpression, MatchesNull) {
    RegexMatchExpression regex;
    ASSERT(regex.init("a", "b", "").isOK());
    ASSERT(!regex.matchesBSON(BSONObj(), NULL));
    ASSERT(!regex.matchesBSON(BSON("a" << BSONNULL), NULL));
}
TEST(RegexMatchExpression, MatchesNull) {
    RegexMatchExpression regex;
    ASSERT(regex.init("a", "b", "").isOK());
    ASSERT(!regex.matchesBSON(BSONObj(), NULL));
    ASSERT(!regex.matchesBSON(BSON("a" << BSONNULL), NULL));
}