why kotlin lambda decompiled to java code is (Function0)null.INSTANCE

when I declare a property in a class as following:

class xx{
    var b:()->Boolean={false}
}

and then decompiled as following:

......

public xxx() {
    this.b = (Function0)null.INSTANCE;
}

......

what does the (Function0)null.INSTANCE stand for? I think it will be :

this.b= new Function0() {
        public final Object invoke() {
                 return false;
         }
};

but it doesn't ,why?

Thanks!