there may be a issue with one of the tests in mux_test

[helios741]

in mux_test.go#L1469

1 func TestMuxRegexp2(t *testing.T) {
2	r := NewRouter()
3	r.Get("/foo-{suffix:[a-z]{2,3}}.json", func(w http.ResponseWriter, r *http.Request) {
4		w.Write([]byte(URLParam(r, "suffix")))
5	})
6	ts := httptest.NewServer(r)
7	defer ts.Close()
8
9	if _, body := testRequest(t, ts, "GET", "/foo-.json", nil); body != "" {
10		t.Fatalf(body)
11	}
12	if _, body := testRequest(t, ts, "GET", "/foo-abc.json", nil); body != "abc" {
13		t.Fatalf(body)
14	}
15}

I don't think the /foo-.json in line 9 matches the /foo-{suffix:[a-z]{2,3}}.json in line 3.
because "" does not satisfy [a-z]{2,3}.or what is the original purpose of this design.
this question is similar to #609.

[helios741]

If it's a issue, I can fix it uniformly