52 In that respect, the Court has already held that it is legitimate for a Member State to wish to protect the special relationship of solidarity and good faith between it and its nationals and also the reciprocity of rights and duties, which form the bedrock of the bond of nationality (judgments of 2 March 2010, Rottmann, C‑135/08, EU:C:2010:104, paragraph 51, and of 12 March 2019, Tjebbes and Others, C‑221/17, EU:C:2019:189, paragraph 33). 53 In the present case, as the Austrian Government has pointed out and as is apparent from Paragraph 10(3) of the StbG, the purpose of that law is, inter alia, to avoid one person having multiple nationalities. Paragraph 20(1) of that law is one of the provisions intended precisely to achieve that objective. 54 In that regard, it should be noted, first, that, in the exercise of its powers to lay down the conditions for the acquisition and loss of its nationality, it is legitimate for a Member State, such as the Republic of Austria, to take the view that the undesirable consequences of one person having multiple nationalities should be avoided. 55 The legitimacy, in principle, of that objective is borne out by Article 15(b) of the European Convention on Nationality, according to which the provisions of that convention do not limit the right of each State party to determine in its internal law whether the acquisition or retention of its nationality is subject to the renunciation or to the loss of another nationality. As the Advocate General observed, in essence, in point 92 of his Opinion, that legitimacy is further supported by Article 7(2) of the Convention on the Reduction of Statelessness, according to which a national of a contracting State who seeks naturalisation in a foreign country is not to lose his or her nationality unless that person acquires or has been accorded assurance of acquiring the nationality of that foreign country. 56 Secondly, Paragraph 20(2) of the StbG provides that the assurance as to the grant of Austrian nationality is to be revoked where the person concerned no longer fulfils any one of the requirements for that grant. Among those requirements is that laid down in point 6 of Paragraph 10(1) of the StbG, according to which the person concerned must, on the basis of his or her conduct hitherto, guarantee that he or she has a positive attitude towards the Republic of Austria and neither represents a danger to law and order or public security nor endangers other public interests as referred to in Article 8(2) of the European Convention for the Protection of Human Rights and Fundamental Freedoms. 57 The decision to revoke the assurance as to the grant of nationality on the ground that the person concerned does not have a positive attitude towards the Member State of which he or she wishes to acquire the nationality and that his or her conduct is liable to represent a danger to public order and security of that Member State is based on a reason relating to the public interest (see, by analogy, judgment of 2 March 2010, Rottmann, C‑135/08, EU:C:2010:104, paragraph 51). 58 That said, having regard to the importance which primary law attaches to the status of citizen of the Union which, as has been pointed out in paragraphs 38 and 46 above, constitutes the fundamental status of nationals of the Member States, it is for the competent national authorities and the national courts to ascertain whether the decision to revoke the assurance as to the grant of nationality, when it entails the loss of the status of citizen of the Union and of the rights attaching thereto, has due regard to the principle of proportionality so far as concerns the consequences it entails for the situation of the person concerned and, if relevant, for the members of his or her family, from the point of view of EU law (see, by analogy, judgments of 2 March 2010, Rottmann, C‑135/08, EU:C:2010:104, paragraphs 55 and 56, and of 12 March 2019, Tjebbes and Others, C‑221/17, EU:C:2019:189, paragraph 40). 59 Examination of whether the principle of proportionality enshrined in EU law was observed requires an individual assessment of the situation of the person concerned and, if relevant, that of his or her family in order to determine whether the consequences of the decision to revoke the assurance as to the grant of nationality, when it entails the loss of the status of citizen of the Union, might, with regard to the objective pursued by the national legislature, disproportionately affect the normal development of his or her family and professional life from the point of view of EU law. Those consequences cannot be hypothetical or merely a possibility (see, by analogy, judgment of 12 March 2019, Tjebbes and Others, C‑221/17, EU:C:2019:189, paragraph 44).