class Shoulda::Matchers::ActiveRecord::HaveDbColumnMatcher

def correct_null?
  return true unless @options.key?(:null)
  if matched_column.null.to_s == @options[:null].to_s
    true
  else
    @missing = "#{model_class} has a db column named #{@column} " <<
               "of null #{matched_column.null}, " <<
               "not #{@options[:null]}."
    false
  end
end