diff --git a/builtin-string.go b/builtin-string.go
index 1ac0f6b..a02b4c8 100644
--- a/builtin-string.go
+++ b/builtin-string.go
@@ -25,7 +25,7 @@ func doJoinStr(funcName string, sep string, it Iterator) (result any, err error)
 			return
 		}
 	}
-	if err == nil || err == io.EOF {
+	if err == io.EOF {
 		err = nil
 		result = sb.String()
 	}