Fix NPE in test util.

sip/addr_test.go

@@ -155,5 +155,9 @@ func TestReversed(t *testing.T) {
 }
 
 func addrError(t *testing.T, name string, want, got *sip.Addr) {
-	t.Errorf("%s:\n%#v\n%#v\n!=\n%#v\n%#v", name, want, want.Uri, got, got.Uri)
+	if want != nil && got != nil {
+		t.Errorf("%s:\n%#v\n%#v\n!=\n%#v\n%#v", name, want, want.Uri, got, got.Uri)
+	} else {
+		t.Errorf("%s:\n%#v\n!=\n%#v", name, want, got)
+	}
 }