Regular expression syntax for "match nothing"?

I have a python template engine that heavily uses regexp. It uses concatenation like: re.compile( regexp1 + "|" + regexp2 + "*|" + regexp3 + "+" ) I can modify the individual substrings (regexp1, regexp2 etc). Is there any small and light expression that matches nothing, which I can use inside a template where I don't want any matches? Unfortunately, sometimes '+' or '*' is appended to the regexp

[knjname]

@knjname $^ や a^ ね。考えつかなかった。あと(?!)だけでもいいのか。そっか。