Exception throw when compiling a project: java.lang.NullPointerException: tried to cast away nullability, but value is null

[OndrejSpanel]

Compiler version

3.1.3

Minimized example

I am afraid I do not have a minimized example yet, I will need some advice on how to extract it.

I am trying to port my complex project to Scala 3. I have fixed most deprecation warnings in 2.13 and upgraded almost all libraries. I am not getting much compiler errors any more, but still use both "-source:3.0-migration" and "-Xignore-scala2-macros", as not all libraries are ported and I still need to compile the project as 2.13 one.

Output

When building my project with Scala 3.1.3, I get following error:

Exception when compiling 382 sources to ....... java.lang.NullPointerException: tried to cast away nullability, but value is null

I am not told which part of the project / what particulat Scala source is the compiler working at, therefore I have no idea how could I pinpoint the problem.

The top of the callstack is:

[error] java.lang.NullPointerException: tried to cast away nullability, but value is null
[error] scala.runtime.Scala3RunTime$.nn(Scala3RunTime.scala:19)
[error] dotty.tools.dotc.core.OrderingConstraint.swapKey$1(OrderingConstraint.scala:495)
[error] dotty.tools.dotc.core.OrderingConstraint.subst(OrderingConstraint.scala:496)
[error] dotty.tools.dotc.core.OrderingConstraint.subst(OrderingConstraint.scala:494)
[error] dotty.tools.dotc.core.TyperState.ensureNotConflicting$$anonfun$1(TyperState.scala:181)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.core.TyperState.ensureNotConflicting(TyperState.scala:182)
[error] dotty.tools.dotc.core.TyperState.mergeConstraintWith(TyperState.scala:193)
[error] dotty.tools.dotc.core.TyperState.commit(TyperState.scala:163)
[error] dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:3111)
[error] dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:1002)
[error] dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:1040)
[error] dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:327)
[error] dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:117)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2832)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2895)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3080)
[error] dotty.tools.dotc.typer.Typer.$anonfun$47(Typer.scala:2278)
[error] dotty.tools.dotc.typer.PrepareInlineable$.dropInlineIfError(PrepareInlineable.scala:248)
[error] dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:2278)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2808)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2894)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2986)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2476)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2820)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2824)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2894)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2986)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2476)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2820)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2824)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2894)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2986)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2603)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2865)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2895)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3013)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2603)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2865)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2895)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3080)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:43)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$adapted$1(TyperPhase.scala:50)
[error] scala.Function0.apply$mcV$sp(Function0.scala:39)
[error] dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:414)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:50)
[error] dotty.tools.dotc.typer.TyperPhase.runOn$$anonfun$3(TyperPhase.scala:84)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.typer.TyperPhase.runOn(TyperPhase.scala:84)
[error] dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:225)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1328)
[error] dotty.tools.dotc.Run.runPhases$1(Run.scala:236)```

Expectation

I think compiler can show errors, but should never throw exceptions.