45In particular, the margin of discretion left to the Member States by a provision, for the purpose of ensuring the correct and straightforward application and of preventing any evasion, avoidance or abuse does not preclude that provision from being unconditional. In addition, a Member State may not rely on its failure to adopt the provisions which are intended to apply the rule at issue, as against a taxpayer who is able to show that his or her tax position actually falls within one of the cases laid down in a directive (see, to that effect and by analogy, judgment of 17 July 2008, Flughafen Köln/Bonn, C‑226/07, EU:C:2008:429, paragraph 31 and the case-law cited).