Disable dropping of wrong elements

src/DragGrid.vue

@@ -143,6 +143,7 @@ export default {
     },
     handleDragOver(event) {
       let data = event.dataTransfer.getData("vueDrag/gridItem");
+      if (!data) return;
       let element = JSON.parse(data);
       let coords = this.getCoords(event.layerX, event.layerY);
 
@@ -175,6 +176,7 @@ export default {
     handleDrop(event) {
       this.$refs.highlightContainer.style.display = "none";
       let data = event.dataTransfer.getData("vueDrag/gridItem");
+      if (!data) return;
       let element = JSON.parse(data);
 
       if (this.validateElement) this.validateElement(element);