jwt: claims.go - len(a) == 0 should return nil, false

jwt/claims.go

diff --git a/jwt/claims.go b/jwt/claims.go
index 3f5e07e..0b19368 100644
--- a/jwt/claims.go
+++ b/jwt/claims.go
@@ -124,6 +124,10 @@
 }
 
 func stringify(a ...interface{}) ([]string, bool) {
+	if len(a) == 0 {
+		return nil, false
+	}
+
 	s := make([]string, len(a))
 	for i := range a {
 		str, ok := a[i].(string)