FIX: exception when pressing backspace on empty selection (#7587)

FIX: exception when pressing backspace on empty selection (#7587)

diff --git a/app/assets/javascripts/select-kit/mixins/events.js.es6 b/app/assets/javascripts/select-kit/mixins/events.js.es6
index 167fc22..7c8ac46 100644
--- a/app/assets/javascripts/select-kit/mixins/events.js.es6
+++ b/app/assets/javascripts/select-kit/mixins/events.js.es6
@@ -249,7 +249,7 @@ export default Ember.Mixin.create({
       return;
     }
 
-    if (!this.get("selection").length) return;
+    if (!this.selection || !this.selection.length) return;
 
     if (!Ember.isEmpty(this.get("filter"))) {
       this.clearHighlightSelection();

GitHub sha: cf63a9bb