[FIR] Store fir for invalid when branches

^KTIJ-25646 fixed

Merge-request: KT-MR-10646
Merged-by: Egor Kulikov <Egor.Kulikov@jetbrains.com>

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/impl/FirWhenSubjectExpressionImpl.kt

@@ -27,7 +27,7 @@ internal class FirWhenSubjectExpressionImpl(
     override var annotations: MutableOrEmptyList<FirAnnotation>,
     override val whenRef: FirExpressionRef<FirWhenExpression>,
 ) : FirWhenSubjectExpression() {
-    override val typeRef: FirTypeRef get() = whenRef.value.subject!!.typeRef
+    override val typeRef: FirTypeRef get() = whenRef.value.subject?.typeRef ?: org.jetbrains.kotlin.fir.types.impl.FirImplicitUnitTypeRef(source)
 
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
         annotations.forEach { it.accept(visitor, data) }

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt

@@ -418,7 +418,7 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
 
         impl(whenSubjectExpression) {
             default("typeRef") {
-                value = "whenRef.value.subject!!.typeRef"
+                value = "whenRef.value.subject?.typeRef ?: org.jetbrains.kotlin.fir.types.impl.FirImplicitUnitTypeRef(source)"
                 withGetter = true
             }
             useTypes(whenExpression)