Cannot set property 'id' of null

I guess, in my view, I see a ton of functions returning functions and references in order to get
this.currentBill = firebase.database().ref('Bills');
when you could just write
this.currentBill = angFire.list('Bills');
or make a seperate this.items to hold 'Bills'
this.items = angFire.list('Bills');
then work from there