message: null check for out of bounds
diff: @@ -297,8 +297,13 @@ export default class CardManipulator extends Component {
  let elemBelow = document.elementFromPoint(event.clientX, event.clientY);
  fieldEl.style.visibility = 'visible';
  - let currentDropzone = draggableService.getDropzone();
  + // this can happen when you drag the mouse outside the viewport
  + if (!elemBelow) {
  + return;
  + }
  +
  let dropzoneBelow = elemBelow.closest('.drop-zone');
  + let currentDropzone = draggableService.getDropzone();
  if (currentDropzone !== dropzoneBelow) {
  if (currentDropzone) {
  