__importDefault method may return an object with undefined default property

In my project, I use tslib as the helper library.
Today, I come across a mistake like this:

the error line code that generated by tsc is:

typedocApp = new typedoc_1.default.Application();

and typedoc_1 is defined like this:

var typedoc_1 = tslib_1.__importDefault(require("typedoc"));

So, I readed the code of __importDefault method in tslib:

 __importDefault = function (mod) {
        return (mod && mod.__esModule) ? mod : { "default": mod };
    };

If a mod has __esModule property but does not have default property, such as typedoc, the error described above will be fired.

Start at the __importDefault helper implementation and reproduce the reported case with a module that has __esModule but no default property. Trace the generated import usage shown in the issue and add or update coverage for that case; done means the helper no longer produces the reported undefined default behavior without breaking ordinary CommonJS interop.