Fixes

• allow passing null to the PagedModelAdapter.submitList
  • FIX #834
• a PagedListAdapter is allowed to have placeholders. those placeholders are defined as null
  • introduce an interceptor to specify what item the adapter should provide if an element is still a placeholder.
  • NOTE: old default behavior stays the same, you shall provide an interceptor though if you want working placeholders.
  • NOTE: The IItemList was adjusted to return a nullable Item as this is a requirement for the PagedItemList.
  • FIX #843

Interface Changes

• The IItemList was adjusted to return a nullable Item as this is a requirement for the PagedItemList. This is a breaking change if somebody implements a custom ItemList.