get all cards sometimes failed because the list was undefined

client/lib/dialogWithBoardSwimlaneListCard.js

@@ -23,7 +23,10 @@ export class DialogWithBoardSwimlaneListCard extends DialogWithBoardSwimlaneList
   /** returns all available cards of the current list */
   cards() {
     const list = Lists.findOne(this.selectedListId.get());
-    const ret = list.cards(this.selectedSwimlaneId.get());
+    let ret = {}
+    if (list) {
+      ret = list.cards(this.selectedSwimlaneId.get());
+    }
     return ret;
   }