code: func (v *AppChooserButton) GetHeading() (string, error) {
  	cstr := C.gtk_app_chooser_button_get_heading(v.native())
  	if cstr == nil {
  		return "", nilPtrErr
  	}
  	defer C.free(unsafe.Pointer(cstr))
  	return C.GoString((*C.char)(cstr)), nil
  }
docs: // GetHeading() is a wrapper around gtk_app_chooser_button_get_heading().
  // In case when gtk_app_chooser_button_get_heading() returns a nil string,
  // GetHeading() returns a non-nil error.