As written down in the German constitution , the powers of the vacant office were executed by the current President of the Bundesrat , Jens BÃ hrnsen , until Christian Wulff was elected president on 30 June 2010 . As stipulated by the German constitution , the powers of the vacant office were executed by the current President of the Bundesrat , Jens BÃ hrnsen , until Christian Wulff was elected president on 30 June 2010 .