Return error instead of nil when 'Find' fails

regex/matching.go

@@ -148,7 +148,7 @@ func pruneIndices(indices []Match) []Match {
 func (regex Reg) Find(str string) (Group, error) {
 	match, err := regex.FindNthMatch(str, 1)
 	if err != nil {
-		return Group{}, nil
+		return Group{}, fmt.Errorf("no matches found")
 	}
 	return getZeroGroup(match), nil
 }