急！！！easyui树状菜单找不到节点

function doMenuAssign() {
        var row =$("#role_table").datagrid("getSelected");
            if(row==null || row.length==0){
                return;
            }
            $.ajax({
                url:"role/roleMenu",
                data:"group_code="+row.group_code,
                success:function(menuIds){
                    $("#role-menu-tree").tree({
                    url : "rolePermission/getAllMenu",
                    method : "post",
                    checkbox : true,
                    onLoadSuccess : function(node, data) {
                        for(var i=0;i<menuIds.length;i++){
                            var nodeMenu=$("#role-menu-tree").tree("find",menuIds[i]);
                            if ($("#role-menu-tree").tree("isLeaf",nodeMenu.target)) {
                                $("#role-menu-tree").tree("check",nodeMenu.target);
                            }
                        }
                        $("#role-menu-dialog").dialog("open")
                    }
                    });
                }
            })


        }

var nodeMenu=$("#role-menu-tree").tree("find",menuIds[i]);
这里找不到菜单节点，返回的是null

求大神帮忙看看是什么原因，很急很急，拜托大神们