Verify 'called without prior match' error handling for .sub().

src/tests/sub.vtc

@@ -128,3 +128,44 @@ client c1 {
 	expect resp.http.N-6 == "barbar"
 	expect resp.http.N-7 == "/?foobar=2"
 } -run
+
+varnish v1 -vcl {
+	import ${vmod_selector};
+	import std;
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new s = selector.set();
+		s.add("foo", regex="bar");
+	}
+
+	sub vcl_recv {
+		return (synth(200));
+	}
+
+	sub vcl_synth {
+		set resp.http.Sub = s.sub("foo", "bar");
+		set resp.http.Sub-False = s.sub("foo", "bar", false);
+		set resp.http.Suball = s.sub("foo", "bar", true);
+		return (deliver);
+	}
+}
+
+logexpect l1 -v v1 -d 0 -g vxid -q "VCL_Error" {
+	expect 0 * Begin req
+	expect * = VCL_Error {^vmod selector error: s\.sub\(\) called without prior match$}
+	expect * = VCL_Error {^vmod selector error: s\.sub\(\) called without prior match$}
+	expect * = VCL_Error {^vmod selector error: s\.sub\(\) called without prior match$}
+	expect * = End
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.http.Sub == ""
+	expect resp.http.Sub-False == ""
+	expect resp.http.Suball == ""
+} -run
+
+logexpect l1 -wait