Merge pull request '[fix] dup empty name check ignore' (#2) from fix/empty-key-dup-and-required into master

Reviewed-on: #2

argparse.go

@@ -39,7 +39,7 @@ func New() *Parser {
 
 func (p *Parser) addArg(a *arg) error {
 	for _, v := range p.args {
-		if v.sname == a.sname || v.lname == a.lname {
+		if (a.sname != "" && v.sname == a.sname) || (a.lname != "" && v.lname == a.lname) {
 			return errors.New("option name dup")
 		}
 	}