Registering undefined partial throws exception.

lib/handlebars/base.js

@@ -47,6 +47,9 @@ HandlebarsEnvironment.prototype = {
     if (toString.call(name) === objectType) {
       Utils.extend(this.partials,  name);
     } else {
+      if (typeof partial === 'undefined') {
+        throw new Exception('Attempting to register a partial as undefined');
+      }
       this.partials[name] = partial;
     }
   },

spec/partials.js

@@ -46,6 +46,13 @@ describe('partials', function() {
     }, Handlebars.Exception, 'The partial whatever could not be found');
   });
 
+  it("registering undefined partial throws an exception", function() {
+    shouldThrow(function() {
+      var undef;
+      handlebarsEnv.registerPartial('undefined_test', undef);
+    }, Handlebars.Exception, 'Attempting to register a partial as undefined');
+  });
+
   it("rendering template partial in vm mode throws an exception", function() {
     shouldThrow(function() {
       var template = CompilerContext.compile("{{> whatever}}");