Can someone help me understand how a NullPointerEx...

# android

[Nok Ah]

Can someone help me understand how a NullPointerException (NPE) can occur in the following scenario? I'm using a singleton class instantiated with DI, and I'm encountering an NPE when calling items.find. The exception message is: Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.models.Item.getId()' on a null object reference. How could this be happening?

class ItemRepositoryImpl : ItemRepository {
    private val items = mutableListOf<Item>()

    private fun processItem(inputItem: InputItem?, subject: BehaviorSubject<ItemState>) {
        if (inputItem != null) {
            items.find { it.id == inputItem.itemId }?.let {
                it.markAsProcessed()
                it.isActive = true
            }
            subject.onNext(ItemState.ShowItem(inputItem))
        } else {
            subject.onNext(ItemState.Empty)
        }
    }
}

How could this be causing an NPE when items.find is called?

[Michael Krussel]

It that the whole class, because nothing ever populates items.If there is more happening, could be issues where another thread is getting access to ItemRepositoryImpl before it is fully constructed. Could be that something is casting items to something that allows inserting a null into it.

Another thought is that intrinsics are complaining that Item.id is null because something like a serializer deserialized a null into it.

[Dale Hawkins]

How is the list being populated?

[Nok Ah]

In this case, the list is only being populated once at initiation. BUT, even if the list of items were empty, it doesn't explain the crash since it has started iterating over the cards. Thats atleast what I am thinking

[Brajesh]

is id mapped with your model id?