class ActiveRecord::Relation::WhereClause

def contradiction?
  predicates.any? do |x|
    case x
    when Arel::Nodes::In
      Array === x.right && x.right.empty?
    when Arel::Nodes::Equality
      x.right.respond_to?(:unboundable?) && x.right.unboundable?
    end
  end
end