The process of Decorator has mistake make the PropertyDescriptor with undefined value

[JiaHenry]

Please try with the code in TypeScript Playground

or the source code:
`// @experimentalDecorators
function LogMethod(
target: any,
propertyKey: string | symbol,
descriptor: PropertyDescriptor
) {
console.log(target);
console.log(propertyKey);
console.log(descriptor);
}

class Demo {
@logmethod
public static foo(bar: number) {
// do nothing
}

@logmethod
public foo2(bar: number) {
// do nothing
}
}

const demo = new Demo();
Demo.foo(10);
demo.foo2(12);`

The output of js with something like __decorate(([...], Demo.prototype, "foo2", null)
but the karma-typescript output code like __decorate([LogMethod], Demo.prototype, 'foo2')

the missing null at end will make the code in __decorate as following:
r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc
make the desc keep the undefined value because undefined === null is false.

Please see bellow pictures about the output.
The is the output in TypeScript Playground

And the output of karma