App crashes when combining Flow with a MutableStateFlow. Code in :thread:

# coroutines

[ms]

App crashes when combining Flow with a MutableStateFlow.
Code in 🧵

[ms]

val appsFlow: Flow<List<App>>
    get() = appDrawerRepo.allAppsFlow.combine(hiddenAppsRepo.onlyHiddenAppsFlow) { allApps, hiddenApps ->
        allApps.minus(hiddenApps)
    }.combine(searchFlow) { filteredApps, query ->
        when {
            query.isNotEmpty() -> filteredApps.filter {
                it.name.startsWith(
                    query,
                    ignoreCase = true
                )
            }
            else -> filteredApps
        }
    }

[ms]

private val searchAppFlow = MutableStateFlow("")

[ms]

It works if I remove the second combine or use listOf("").asFlow()

[ms]

java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object kotlinx.coroutines.flow.Flow.collect(kotlinx.coroutines.flow.FlowCollector, kotlin.coroutines.Continuation)' on a null object reference
at kotlinx.coroutines.flow.internal.CombineKt$combineInternal$2$1.invokeSuspend(Combine.kt:145)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
at kotlinx.coroutines.EventLoop.processUnconfinedEvent(EventLoop.common.kt:69)
at kotlinx.coroutines.DispatchedTaskKt.resumeUnconfined(DispatchedTask.kt:244)
at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:161)
at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:369)
at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:403)
at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:395)
at kotlinx.coroutines.CancellableContinuationImpl.resumeWith(CancellableContinuationImpl.kt:300)

[natario1]

Maybe you are declaring the searchFlow after appsFlow in your file.

[ephemient]

or in a subclass

[ms]

They both are in same class one after other

[Abhishek Dewan]

Based on the error appDrawerRepo.allAppsFlow seems to be null. are you able to collect that flow in isolation and not using combine ?

[ms]

Yes, I'm unable to use it with combine.
But instead of searchFlow if I give listOf("").asFlow() to combine it works.

[ms]

Even if I use the combine in reverse order, it crashes at the first combine call

[louiscad]

Which kotlinx.coroutines version are you using?

[ephemient]

I think an initialization problem is more likely. you can try to insert a .also { println(searchFlow) } before the .combine(searchFlow) { ... }

[ms]

This is happening for every MutableStateFlow even though I initialized it.
I'm using Jetpack Compose 1.0.0-beta06

[louiscad]

@ms I asked a question.

[ms]

@louiscad I'm using Jetpack Compose, no explicit import

[louiscad]

Are you able to reproduce the issue in a simple JVM program?

[ms]

@louiscad It worked when I tried it in Kotlin Playground. Maybe it's something from Compose side I guess