if ( function_exists( 'oxygen_vsb_register_condition' ) ) {

	oxygen_vsb_register_condition(
		// Condition Name
		'ACF Field Empty',

		// Values: The array of pre-set values the user can choose from.
		// Set the custom key's value to true to allow users to input custom values.
		array( 
			'options' => array(),
			'custom' => true
		),

		// Operators
		array( '--' ),
		
		// Callback Function: Name of function that will be used to handle the condition
		'acf_field_empty_fallback',

		// Condition Category: Default ones are Archive, Author, Other, Post, User
		'ACF'
	);

}

/**
 * Callback function to handle the condition.
 * @param  mixed 	$value    	Input value - in this case, name of ACF custom field.
 * @param  string 	$operator 	Comparison operator selected by the user.
 *
 * @return boolean 				true or false.
 */
function acf_field_empty_fallback( $value, $operator ) {

	return ( get_field( $value ) ) ? false : true;

}