Does European Union law, in particular Articles 18, 45 and 48 of the Treaty on the Functioning of the European Union and Article 7(2) of Regulation (EU) No 492/2011 of the European Parliament and of the Council of 5 April 2011 on freedom of movement for workers within the Union, preclude provisions of the law of a Member State, such as Article 195 of the Luxembourg Social Security Code and Articles 3, 4 and 4-1 of the amended Law of 9 July 2004 on the legal effects of certain partnerships, which make the grant, to the surviving partner of a partnership properly entered into and registered in the Member State of origin, of a survivor’s pension, due as a result of the exercise by the deceased partner of a professional activity in the host Member State, subject to the condition that the partnership was recorded in a register kept by that State for the purposes of verifying compliance with the substantive conditions required by the law of that Member State in order to recognise a partnership and ensure its effectiveness visà-vis third parties, whereas the grant of a survivor’s pension to the surviving partner of a partnership entered into in the host Member State is subject to the sole condition that the partnership has been properly entered into and registered there?