SOCIAL POLICY - APPROXIMATION OF LAWS - TRANSFERS OF UNDERTAKINGS - SAFEGUARDING OF EMPLOYEES ' RIGHTS - DIRECTIVE NO 77/187 - TRANSFEREE ' S OBLIGATIONS REGARDING HOLIDAY PAY - EXISTENCE OF A CONTRACT OF EMPLOYMENT ON THE DATE OF THE TRANSFER - TO BE ESTABLISHED ACCORDING TO NATIONAL LAW ( COUNCIL DIRECTIVE NO 77/187 , ARTS 3 ( 1 ) AND 4 ( 1 ))