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

docs/change-log.md

@@ -28,6 +28,7 @@
 - API: `m.route.set()` causes all mount points to be redrawn ([#1592](https://github.com/MithrilJS/mithril.js/pull/1592))
 - API: If a user sets the Content-Type header within a request's options, that value will be the entire header value rather than being appended to the default value ([#1924](https://github.com/MithrilJS/mithril.js/pull/1924))
 - API: Using style objects in hyperscript calls will now properly diff style properties from one render to another as opposed to re-writing all element style properties every render.
+- Fix IE11 active element is null causing render function to throw error.
 
 ---
 

render/render.js

@@ -630,7 +630,7 @@ 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()
+		if (active !== null && $doc.activeElement !== active) active.focus()
 	}
 
 	return {render: render, setEventCallback: setEventCallback}