code: func (v *Widget) GetTooltipText() (string, error) {
  	c := C.gtk_widget_get_tooltip_text(v.native())
  	if c == nil {
  		return "", nilPtrErr
  	}
  	return C.GoString((*C.char)(c)), nil
  }
docs: // GetTooltipText is a wrapper around gtk_widget_get_tooltip_text().
  // A non-nil error is returned in the case that
  // gtk_widget_get_tooltip_text returns NULL to differentiate between NULL
  // and an empty string.