reject!()
Equivalent to Hash#delete_if, but returns nil if no changes were made.
VALUE rb_hash_reject_bang(VALUE hash) { int n; RETURN_ENUMERATOR(hash, 0, 0); if (!RHASH(hash)->ntbl) return Qnil; n = RHASH(hash)->ntbl->num_entries; rb_hash_delete_if(hash); if (n == RHASH(hash)->ntbl->num_entries) return Qnil; return hash; }