Решение состоит в том, чтобы разбить ваши выражения на множество выражений, например, попробуйте заменить:
return Council(status: status ?? self.status,
council : council ?? self.council,
year: year ?? self.year,
councilRating: councilRating ?? self.councilRating,
annualChange: annualChange ?? self.annualChange,
councilTax: councilTax ?? self.councilTax)
на:
let s = status ?? self.status
let c = council ?? self.council
let y = year ?? self.year
let cr = councilRating ?? self.councilRating
let ac = annualChange ?? self.annualChange
let ct = councilTax ?? self.councilTax
return Council(status: s,
council : c,
year: y,
councilRating: cr,
annualChange: ac,
councilTax: ct)