don't throw error when using console.log in firefox

mithril.js

@@ -91,7 +91,7 @@ var m = (function app(window, undefined) {
 		//there's logic that relies on the assumption that null and undefined data are equivalent to empty strings
 		//- this prevents lifecycle surprises from procedural helpers that mix implicit and explicit return statements (e.g. function foo() {if (cond) return m("div")}
 		//- it simplifies diffing code
-		if (data == null) data = "";
+		if (data == null || data.toString() == null) data = "";
 		if (data.subtree === "retain") return cached;
 		var cachedType = type.call(cached), dataType = type.call(data);
 		if (cached == null || cachedType !== dataType) {

tests/mithril-tests.js

@@ -795,6 +795,11 @@ function testMithril(mock) {
 		m.render(root, m("div", [m("div", 1), null, [m("div", {key: 3}, 3), m("div", {key: 4}, 4), m("div", {key:5}, 5)], [m("div", {key: 6}, 6)]]))
 		return root.childNodes[0].childNodes.map(function(c) {return c.childNodes ? c.childNodes[0].nodeValue: c.nodeValue}).slice(0, 5).join("") == "13456"
 	})
+	test(function() {
+		var root = mock.document.createElement("div")
+		m.render(root, m("div", [console.log()])) //don't throw in Firefox
+		return true
+	})
 	//end m.render
 
 	//m.redraw