Return error instead of panicking if the range cannot be processed

range2regex.go

@@ -44,11 +44,11 @@ func intToSlc(val int) []int {
 	return toRet
 }
 
-func range2regex(start int, end int) string {
+func range2regex(start int, end int) (string, error) {
 	rangeStart := start
 	rangeEnd := end
 	if rangeStart > rangeEnd {
-		panic("Range start greater than range end.")
+		return "", fmt.Errorf("numeric range start greater than range end")
 	}
 
 	ranges := make([]numRange, 0)
@@ -121,6 +121,6 @@ func range2regex(start int, end int) string {
 		regex += ")"
 	}
 	regex += ")"
-	return regex
+	return regex, nil
 
 }