defensive check

src/dagre/util.js

@@ -92,6 +92,7 @@ function predecessorWeights(g) {
  * ({x, y, width, height}) if it were pointing at the rectangle's center.
  */
 function intersectRect(rect, point) {
+  if (!rect|| !point) return { x: 0, y: 0 };
   var x = rect.x;
   var y = rect.y;