epoxy: [epoxy-paging] Crash in the PagedListEpoxyController when trying to invoke `addTo` on a null model

While trying to implement paged list + paged controller, I run into a crash that’s not reliably reproducible. The crash seems to happen around 1 in 7 times, completely anecdotally.

I’m attaching the stack trace: note how my custom controller (that extends PagedListEpoxyController) is not in the stack trace because the crash happens in PagedListEpoxyController internals.

I will try to get a small sample app with a reliable reproducible test case. In the meantime, some information that could be useful:

• In MyImplementationPagedListController, I have these two params:
  • modelBuildingHandler = EpoxyAsyncUtil.getAsyncBackgroundHandler()
  • diffingHandler = EpoxyAsyncUtil.getAsyncBackgroundHandler()
• I’m using an RxPagedListBuilder with setFetchScheduler(Schedulers.io())
• The problem reproduces more frequently with a very small page size: I used size 4 on a total list size 22

I noticed that PagedListModelCache holds null models, I am guessing one of those is likely mistakenly being passed through in getModels().

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.airbnb.epoxy.EpoxyModel.addTo(com.airbnb.epoxy.EpoxyController)' on a null object reference
at com.airbnb.epoxy.EpoxyController.add(EpoxyController.java:465)
at com.airbnb.epoxy.paging.PagedListEpoxyController.addModels(PagedListEpoxyController.kt:78)
at com.airbnb.epoxy.paging.PagedListEpoxyController.buildModels(PagedListEpoxyController.kt:70)
at com.airbnb.epoxy.EpoxyController$1.run(EpoxyController.java:267)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.os.HandlerThread.run(HandlerThread.java:61)