reject!()
Equivalent to Hash#delete_if, but returns nil if no changes were made.
VALUE rb_hash_reject_bang(VALUE hash) { st_index_t n; RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size); rb_hash_modify(hash); n = RHASH_SIZE(hash); if (!n) return Qnil; rb_hash_foreach(hash, delete_if_i, hash); if (n == RHASH(hash)->ntbl->num_entries) return Qnil; return hash; }