Hi I have a similar structure in my project, link ...

# flow

[Vaibhav Jaiswal]

Hi
I have a similar structure in my project, link to playground https://pl.kotl.in/WM-fc97xm

abstract class Parent {
    abstract val flow1: StateFlow<Int>
    
    val flow2 = flow1.mapLatest { it.toString() }
    
}

class Child : Parent() {
    override val flow1 = MutableStateFlow(1).asStateFlow()
}

fun main(){
    val child = Child()
    
    runBlocking {
        child.flow2.collect {
            
        }
    }
}

This seems to crash my app, saying
> 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
Also fails on compile in Kotlin Playground

Does anyone know whats wrong
App Crash Stack Trace in 🧵

If i make the 2nd flow also abstract it works

[Vaibhav Jaiswal]

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 referenc
	at kotlinx.coroutines.flow.FlowKt__TransformKt$filterNotNull$$inlined$unsafeTransform$1.collect(SafeCollector.common.kt:109)
	at kotlinx.coroutines.flow.internal.ChannelFlowTransformLatest$flowCollect$3.invokeSuspend(Merge.kt:23)
	at kotlinx.coroutines.flow.internal.ChannelFlowTransformLatest$flowCollect$3.invoke(Unknown Source:8)
	at kotlinx.coroutines.flow.internal.ChannelFlowTransformLatest$flowCollect$3.invoke(Unknown Source:4)
	at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:42)
	at kotlinx.coroutines.CoroutineScopeKt.coroutineScope(CoroutineScope.kt:261)
	at kotlinx.coroutines.flow.internal.ChannelFlowTransformLatest.flowCollect(Merge.kt:21)
	at kotlinx.coroutines.flow.internal.ChannelFlowOperator.collectTo$suspendImpl(ChannelFlow.kt:153)
	at kotlinx.coroutines.flow.internal.ChannelFlowOperator.collectTo(Unknown Source:0)
	at kotlinx.coroutines.flow.internal.ChannelFlow$collectToFun$1.invokeSuspend(ChannelFlow.kt:56)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:102)
	at kotlinx.coroutines.EventLoop.processUnconfinedEvent(EventLoop.common.kt:65)
	at kotlinx.coroutines.internal.DispatchedContinuation.resumeWith(DispatchedContinuation.kt:341)
	at kotlin.coroutines.ContinuationKt.startCoroutine(Continuation.kt:129)
	at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:89)
	at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:124)
	at kotlinx.coroutines.channels.ProduceKt.produce(Produce.kt:129)
	at kotlinx.coroutines.channels.ProduceKt.produce$default(Produce.kt:117)
	at kotlinx.coroutines.flow.internal.ChannelFlow.produceImpl(ChannelFlow.kt:115)
	at kotlinx.coroutines.flow.internal.ChannelFlow$collect$2.invokeSuspend(ChannelFlow.kt:119)
	at kotlinx.coroutines.flow.internal.ChannelFlow$collect$2.invoke(Unknown Source:8)
	at kotlinx.coroutines.flow.internal.ChannelFlow$collect$2.invoke(Unknown Source:4)
	at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:42)
	at kotlinx.coroutines.CoroutineScopeKt.coroutineScope(CoroutineScope.kt:261)
	at kotlinx.coroutines.flow.internal.ChannelFlow.collect$suspendImpl(ChannelFlow.kt:118)
	at kotlinx.coroutines.flow.internal.ChannelFlow.collect(Unknown Source:0)
	at kotlinx.coroutines.flow.internal.ChannelFlowOperator.collect$suspendImpl(ChannelFlow.kt:169)
	at kotlinx.coroutines.flow.internal.ChannelFlowOperator.collect(Unknown Source:0)
	at androidx.paging.FlowExtKt$simpleRunningReduce$1.invokeSuspend(FlowExt.kt:68)
	at androidx.paging.FlowExtKt$simpleRunningReduce$1.invoke(Unknown Source:8)
	at androidx.paging.FlowExtKt$simpleRunningReduce$1.invoke(Unknown Source:4)
	at kotlinx.coroutines.flow.SafeFlow.collectSafely(Builders.kt:57)
	at kotlinx.coroutines.flow.AbstractFlow.collect(Flow.kt:226)
	at androidx.paging.CachedPagingDataKt$cachedIn$$inlined$map$1.collect(SafeCollector.common.kt:113)
	at kotlinx.coroutines.flow.FlowKt__EmittersKt$onStart$$inlined$unsafeFlow$1.collect(SafeCollector.common.kt:116)
	at kotlinx.coroutines.flow.FlowKt__EmittersKt$onCompletion$$inlined$unsafeFlow$1.collect(SafeCollector.common.kt:110)
	at kotlinx.coroutines.flow.FlowKt__ShareKt$launchSharing$1.invokeSuspend(Share.kt:215)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:102)
	at android.os.Handler.handleCallback(Handler.java:958)
	at android.os.Handler.dispatchMessage(Handler.java:99)
	at android.os.Looper.loopOnce(Looper.java:205)
	at android.os.Looper.loop(Looper.java:294)
	at android.app.ActivityThread.main(ActivityThread.java:8177)

                                                                                                    	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:552)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:971)
	Suppressed: kotlinx.coroutines.internal.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@de64853, Dispatchers.Main.immediate]