mixin({} ,x, x) did not clear x, but was meant to

Now slightly changed mixin does it with mixin(null, x, x) call.

brikz.js

@@ -5,8 +5,10 @@ function Brikz(api, apiKey, initKey) {
 
 	function mixin(src, target, what) {
 		for (var keys = Object.keys(what||src), l=keys.length, i=0; i<l; ++i) {
-			var value = src[keys[i]];
-			if (typeof value !== "undefined") { target[keys[i]] = value; }
+			if (src == null) { target[keys[i]] = undefined; } else {
+				var value = src[keys[i]];
+				if (typeof value !== "undefined") { target[keys[i]] = value; }
+			}
 		}
 		return target;
 	}
@@ -17,13 +19,13 @@ function Brikz(api, apiKey, initKey) {
 
 	this.rebuild = function () {
 		Object.keys(backup).forEach(function (key) {
-			mixin({}, api, (backup[key]||0)[apiKey]);
+			mixin(null, api, (backup[key]||0)[apiKey]||{});
 		});
 		var oapi = mixin(api, {}), order = [], chk = {};
 		brikz.ensure = function(key) {
 			if (key in exclude) { return null; }
 			var b = brikz[key], bak = backup[key];
-			mixin({}, api, api);
+			mixin(null, api, api);
 			while (typeof b === "function") { b = new b(brikz, api, bak); }
 			if (b && !chk[key]) { chk[key]=true; order.push(b); }
 			if (b && !b[apiKey]) { b[apiKey] = mixin(api, {}); }
@@ -31,7 +33,7 @@ function Brikz(api, apiKey, initKey) {
 		};
 		Object.keys(brikz).forEach(function (key) { brikz.ensure(key); });
 		brikz.ensure = null;
-		mixin(oapi, mixin({}, api, api));
+		mixin(oapi, mixin(null, api, api));
 		order.forEach(function(brik) { mixin(brik[apiKey] || {}, api); });
 		order.forEach(function(brik) { brik[initKey] && brik[initKey](); });
 		backup = mixin(brikz, {});