May Directive 92/12/EEC, in the light of the general principles of EU law and, in particular, the principles of effectiveness, legal certainty and proportionality thereof, be interpreted, in a case such as this, as prohibiting the implementation of legal provisions of a Member State, such as Article 108 of the Greek Customs Code, according to which the authorised warehousekeeper of goods moved from the tax warehouse thereof under a duty suspension arrangement, which departed the arrangements in question irregularly through smuggling, may be declared as jointly liable for the payment of administrative fines, on the ground of smuggling, regardless of whether the warehousekeeper had, at the time when the infringement was committed, possession of the goods, on the basis of the rules of private law, and, furthermore, regardless of whether the perpetrators of the infringement involved in that movement had concluded a particular contractual relationship with the authorised warehousekeeper from which they can be seen to have acted as agents of the authorised warehousekeeper?