jstree drag and drop on root level is not possible

[Killua Zoldyck]

I'm using jsTree for the first time and everything is going well, the dnd plugin works fine except for dragging nodes to the root level.

After searching for a solution, I only find answers for how to NOT drop a node on the root level.

Dropping nodes (even root nodes) into a parent node is no problem. But I can't drop a node at root level, although with check_callback : true, there should be no problem.

Beneath I'll paste the config of the tree.

Does anyone have an idea what could be wrong?

         'core' : {
            'data' : {
                'url' : '/management/categories/load',
                'data' : {'objectContext' : objectContext},
                'dataType': 'json'
            },
            'check_callback' : true,
            'multiple' : false,
            'themes' : {
                dots : false,
                variant : 'large'
            }
        },
        'plugins' : ['dnd', 'state', 'wholerow', 'types', 'crrm', 'sort'],
        'types' : {
            'default' : {
                'icon' : 'fa fa-folder'
            },
            'folder-open' : {
                'icon' : 'fa fa-folder-open'
            },
            'folder-close' : {
                'icon' : 'fa fa-folder'
            }
        },
        'dnd' : {
            'large_drag_target' : true,
            'large_drop_target' : true 
        }, 
        'sort' : function(a, b) {
            return this.get_node(a).original.position > this.get_node(b).original.position ? 1 : -1;
        }

[Derrick Keith]

Looks good to me  ---> "large_drop_target":"true". 

 'core' : {
            'data' : {
                'url' : '/management/categories/load',
                'data' : {'objectContext' : objectContext},
                'dataType': 'json'
            },
            'check_callback' : true,
            'multiple' : false,
            'themes' : {

                dots : false, //should be "dots": false
                variant : 'large' //should be "variant": "large"