[Interop] Fix assignment of nulls to pointer fields

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/InteropCallConvertors.kt

@@ -194,9 +194,13 @@ private fun InteropCallContext.convertCPointerToNativePtr(cPointer: IrExpression
 }
 
 
-private fun InteropCallContext.writePointerToMemory(nativePtr: IrExpression, value: IrExpression): IrExpression {
+private fun InteropCallContext.writePointerToMemory(
+        nativePtr: IrExpression,
+        value: IrExpression,
+        pointerType: IrType
+): IrExpression {
     val valueToWrite = when {
-        value.type.isCPointer() -> convertCPointerToNativePtr(value)
+        pointerType.isCPointer() -> convertCPointerToNativePtr(value)
         else -> error("Unsupported pointer type")
     }
     return writeValueToMemory(nativePtr, valueToWrite)
@@ -284,7 +288,7 @@ private fun InteropCallContext.generateMemberAtAccess(callSite: IrCall): IrExpre
             when {
                 type.isCEnumType() -> writeEnumValueToMemory(fieldPointer, value)
                 type.isStoredInMemoryDirectly() -> writeValueToMemory(fieldPointer, value)
-                type.isCPointer() -> writePointerToMemory(fieldPointer, value)
+                type.isCPointer() -> writePointerToMemory(fieldPointer, value, type)
                 else -> error("Cannot set field of type ${type.getClass()?.name}")
             }
         }

backend.native/tests/interop/basics/structs.kt

@@ -15,6 +15,9 @@ fun main() {
         assertEquals(next, null)
         next = this.ptr
         assertEquals(next, this.ptr)
+        // Check null pointer because it has Nothing? type.
+        next = null
+        assertEquals(next, null)
 
         assertEquals(vec4f, vectorOf(1.0f, 1.0f, 1.0f, 1.0f))
         vec4f = vectorOf(0.0f, 0.0f, 0.0f, 0.0f)