title: Problems with Fancytree drag-and-drop
body: <p>I am using Fancytree with generally good results. However, I have found a problem with DND. If preventNonNodes is set to true, then my dragEnter function routine is never called. There is a line of code that reads "if (dndOpts.preventNonNodes &amp;&amp; !nodeData)". In practice, noneData is always undefined. If preventNonNodes is true, then the dragEnter() routine is never called? What am I doing wrong here. Should this question be posted over on GitHub?</p>
  
  <p>Below is some code that works. The dragEnter routine is invoked.</p>
  
  <pre><code>    /* Provide some options and routines for drag-and-drop */
      dnd5: {
        /* Expand nodes after n milliseconds of hovering - default */
        autoExpandMS: 1500,      
        /* Absolute position offset for .fancytree-drop-marker - default */
        /* Relative to ..fancytree-title (icon/img near a node accepting drop) */
        dropMarkerOffsetX: -24,  
        /* Additional offset for drop-marker with hitMode = "before"/"after" - default*/
        dropMarkerInsertOffsetX: -16, 
        /* true: Drag multiple (i.e. selected) nodes - default is false*/
        multiSource: false,                
        /* Prevent dropping nodes from different Fancytrees - default is false */
        preventForeignNodes: true,   
        /* Prevent dropping items other than Fancytree nodes - default is false */
        preventNonNodes: false,       
        /* Prevent dropping nodes on own descendants - default */
        preventRecursiveMoves: true,  
        /* Prevent dropping nodes 'before self', etc. - default */
        preventVoidMoves: true,     
        /* Enable auto-scrolling while dragging - default */
        scroll: true,        
        /* Active top/bottom margin in pixel - default */
        scrollSensitivity: 20,        
        /* Pixels per event - default */
        scrollSpeed: 5,               
        /* Events (drag support) */
        dragStart: function (node, data) {
          console.log('dragStart');
          return true;
        },
        dragDrag: function (node, data) {
          console.log('dragDrag');
        }, 
        dragEnd: function (node, data) {
          console.log('dragEnd');
        },         
        /* Events (drop support) */
        dragEnter: function (node, data) {
          console.log('dragEnter');
          return true;
        },      
        dragOver: function (node, data) {
          console.log('dragOver');
        },     
        dragExpand: function (node, data) {
          console.log('dragExpand');
          return true;
        },      
        dragDrop: function (node, data) {
          console.log('dragDrop');
        },
        dragLeave: function (node, data) {
          console.log('dragLeave');
        }
      },
  </code></pre>