Question: An election for the leadership of the Ulster Unionist Party (UUP) was held on 8 April 2017 at the party's Annual General Meeting, the 2017 contested election was triggered after incumbent Leader Mike Nesbitt, elected in 2012, announced following the 2017 assembly election his intention to step down as party leader, the 2017 election to the Northern Ireland Assembly was held on which date?
Sentence (from "Northern Ireland Assembly election, 2017"): It was the sixth election since the Assembly was re-established in 1998, and the first to implement a reduction in size to 90 MLAs (versus the previous 108).
Relevant evidence: No