Fixing IE bug causing active element to be null causing render function to throw error

docs/change-log.md

@@ -10,6 +10,13 @@
 
 ---
 
+### v1.1.4
+
+#### Bug fixes:
+- Fix IE bug where active element is null causing render function to throw error. ([1943](https://github.com/MithrilJS/mithril.js/pull/1943))
+
+---
+
 ### v1.1.3
 
 #### Bug fixes:

render/render.js

@@ -622,7 +622,8 @@ module.exports = function($window) {
 		updateNodes(dom, dom.vnodes, Vnode.normalizeChildren(vnodes), false, hooks, null, namespace === "http://www.w3.org/1999/xhtml" ? undefined : namespace)
 		dom.vnodes = vnodes
 		for (var i = 0; i < hooks.length; i++) hooks[i]()
-		if ($doc.activeElement !== active) active.focus()
+		// document.activeElement can return null in IE https://developer.mozilla.org/en-US/docs/Web/API/Document/activeElement
+		if (active != null && $doc.activeElement !== active) active.focus()
 	}
 
 	return {render: render, setEventCallback: setEventCallback}