[JS IR BE] Fix lowering types nullability

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt

@@ -426,7 +426,7 @@ private fun IrFunction.generateDefaultsFunctionImpl(
         syntheticParameters += newFunction.valueParameter(
             syntheticParameters.last().index + 1,
             "handler".synthesizedName,
-            context.irBuiltIns.anyType
+            context.irBuiltIns.anyNType
         )
     }
 

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/CallableReferenceLowering.kt

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.IrTypeProjection
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
+import org.jetbrains.kotlin.ir.types.makeNullable
 import org.jetbrains.kotlin.ir.util.isInlined
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
@@ -326,7 +327,7 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
             // }
             //
             val cacheName = "${factoryFunction.name}_${Namer.KCALLABLE_CACHE_SUFFIX}"
-            val type = factoryFunction.returnType
+            val type = factoryFunction.returnType.makeNullable()
             val irNull = { JsIrBuilder.buildNull(context.irBuiltIns.nothingNType) }
             val cacheVar = JsIrBuilder.buildVar(type, factoryFunction.parent, cacheName, true, initializer = irNull())