Disabling settings.color.duotone within theme.json causes fatal error

After 5.9.1 update I’ve got this:

When I change “duotone” setting within my theme.json it causes fatal error on site Undefined variable $filters

// theme.json
{
   "version": 2,
   "settings": {
        "color": {
	    "duotone": null
        }
    }
}

Error comes here – https://github.com/WordPress/WordPress/blob/master/wp-includes/class-wp-theme-json.php#L1597

As my duotone is empty, it skips definition of $filters variable

Quick fix: relocate $filters = '' before if ( empty( $node['color']['duotone'] ) ) { condition