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kotlinlang

After updating Kotlin from *1.3.10* to *1.3.50* for a Kotlin Native project, and running the project as a program a strange error appears:
```
type Nothing? is not supported here: doesn't correspond to any C type
```

Double checked the mapping (in the knm file) and found that the return type is `CPointer&lt;gtk3.GtkWidget&gt;?` for the function (`gtk_file_chooser_dialog_new`) that is called in the program. However the function definition looks very odd:
```
@kotlinx.cinterop.internal.CCall public external fun gtk_file_chooser_dialog_new(@kotlinx.cinterop.internal.CCall.CString title: kotlin.String?, parent: kotlinx.cinterop.CValuesRef&lt;gtk3.GtkWindow /* = gtk3._GtkWindow */&gt;?, action: gtk3.GtkFileChooserAction, @kotlinx.cinterop.internal.CCall.CString first_button_text: kotlin.String?, vararg variadicArguments: kotlin.Any?): kotlinx.cinterop.CPointer&lt;gtk3.GtkWidget /* = gtk3._GtkWidget */&gt;? { /* compiled code */ }
```

Below is the piece of code that contains the function call:
```
    private fun createOpenDialog(parent: CPointer&lt;GtkWindow&gt;?) = gtk_file_chooser_dialog_new(
        parent = parent,
        title = "Open File",
        first_button_text = "gtk-cancel",
        action = GtkFileChooserAction.GTK_FILE_CHOOSER_ACTION_OPEN,
        variadicArguments = *arrayOf(GTK_RESPONSE_CANCEL, "gtk-open", GTK_RESPONSE_ACCEPT, null)
    )
```

AFAIK vararg functions are now unsupported by `cinterop`

What is the migration path from vararg functions?

in your case its trivial, just explicitly pass `GTK_RESPONSE_CANCEL, "gtk-open", GTK_RESPONSE_ACCEPT, null` as arguments

This is the new definition where positional parameters are now being used (in the `gtk_file_chooser_dialog_new` function):
```
    private fun createOpenDialog(parent: CPointer&lt;GtkWindow&gt;?) = gtk_file_chooser_dialog_new(
        "Open File",
        parent,
        GtkFileChooserAction.GTK_FILE_CHOOSER_ACTION_OPEN,
        "gtk-cancel",
        GTK_RESPONSE_CANCEL,
        "gtk-open",
        GTK_RESPONSE_ACCEPT,
        null
    )
```
Is this the correct way to do it? Ran the project as a program again and the same error message appears:
```
e: /home/napperley/idea_projects/kpad/src/linuxMain/kotlin/org/example/kpad/Controller.kt: (103, 9): type Nothing? is not supported here: doesn't correspond to any C type
```

Appears as though the compiler is objecting to `null` being passed through as a parameter to the C function (`gtk_file_chooser_dialog_new`), very strange.

Please use properly-typed `null`, e.g. `null as COpaquePointer?`.