Do not export null as module.exports in amd.js. Resolves #2332.

src/extras/amd.js

@@ -56,7 +56,9 @@ import { errMsg } from '../err-msg.js';
           var amdResult = amdExec.apply(exports, depModules);
           if (amdResult !== undefined)
             module.exports = amdResult;
-          _export(module.exports);
+          // https://github.com/systemjs/systemjs/issues/2332
+          if (module.exports !== null)
+            _export(module.exports);
           _export('default', module.exports);
         }
       };

src/extras/named-exports.js

@@ -30,7 +30,7 @@
       // hook the _export function to note the default export
       var defaultExport, hasDefaultExport = false;
       var declaration = registerDeclare.call(this, function (name, value) {
-        if (typeof name === 'object' && name.__useDefault)
+        if (typeof name === 'object' && name && name.__useDefault)
           defaultExport = name.default, hasDefaultExport = true;
         else if (name === 'default')
           defaultExport = value;

src/system-core.js

@@ -112,7 +112,7 @@ export function getOrCreateLoad (loader, id, firstParentUrl) {
           }
         }
 
-        if (name.__esModule) {
+        if (name && name.__esModule) {
           ns.__esModule = name.__esModule;
         }
       }

test/browser/amd.js

@@ -82,4 +82,11 @@ suite('AMD tests', function () {
       assert.equal(m.default, false);
     });
   });
+
+  // https://github.com/systemjs/systemjs/issues/2332
+  test('loading an AMD module that sets module.exports to null', function () {
+    return System.import('fixtures/amd-null-module.js').then(function (m) {
+      assert.equal(m.default, null);
+    });
+  });
 });

test/fixtures/browser/amd-null-module.js

@@ -0,0 +1,3 @@
+define([], function () {
+  return null;
+});