Fix `0` as itemKey issue

[bennobuilder]

🐛 Bug report

🤖 Current Behavior

If you have a Collection and have an Item with the itemKey 0..
it will have problems with this itemKey because we often do

if(!itemKey)
// ..

instead of

if(itemKey == null)
// ..

🎯 Expected behavior

Shouldn't be a problem having an itemKey called 0

💻 Your environment

Software	Version(s)
@agile-ts/core	0.0.15

[bennobuilder]

should be fixed now