FIX: document.activeElement can be null on IE11 (#9880)

FIX: document.activeElement can be null on IE11 (#9880)

diff --git a/app/assets/javascripts/discourse/app/controllers/composer.js b/app/assets/javascripts/discourse/app/controllers/composer.js
index 4890db3..f76b948 100644
--- a/app/assets/javascripts/discourse/app/controllers/composer.js
+++ b/app/assets/javascripts/discourse/app/controllers/composer.js
@@ -1175,7 +1175,7 @@ export default Controller.extend({
     const elem = document.querySelector("html");
     elem.classList.remove("fullscreen-composer");
 
-    document.activeElement.blur();
+    document.activeElement && document.activeElement.blur();
     this.setProperties({ model: null, lastValidatedAt: null });
   },
 

GitHub sha: 675e9b81

This commit appears in #9880 which was merged by jjaffeux.