The only contested seat in the May 20 election, so far, is for the Board of Assessors, according to Town Clerk Janet Bennett. Richard O’Donnell took out papers to run against incumbent Richard Morris for the three-year position, Bennett said. No one took out papers to run against incumbent Selectmen John Brannan and John Reilly, she said. School Committee members David Twombly and Marianne Harte also have no opposition, and nobody filed to run for the open five-year seat on the Planning Board. Any candidates for that spot will have to run a write-in campaign, she said. Candidates have until Tuesday to return their papers.