diff --git a/func-string.go b/func-string.go
index cea9d36..3c6bccb 100644
--- a/func-string.go
+++ b/func-string.go
@@ -184,7 +184,7 @@ func splitStrFunc(ctx ExprContext, name string, args []any) (result any, err err
 func ImportStringFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("joinStr", newGolangFunctor(joinStrFunc), typeString, []ExprFuncParam{
 		newFuncParam(paramSeparator),
-		newFuncParamFlagDef(paramItem, pfOptional|pfRepeat, ""),
+		newFuncParamFlag(paramItem, pfRepeat),
 	})
 
 	ctx.RegisterFunc("subStr", newGolangFunctor(subStrFunc), typeString, []ExprFuncParam{