class ActiveRecord::ConnectionAdapters::MySQL::SchemaCreation

def add_column_options!(sql, options)
  # By default, TIMESTAMP columns are NOT NULL, cannot contain NULL values,
  # and assigning NULL assigns the current timestamp. To permit a TIMESTAMP
  # column to contain NULL, explicitly declare it with the NULL attribute.
  # See https://dev.mysql.com/doc/refman/en/timestamp-initialization.html
  if /\Atimestamp\b/.match?(options[:column].sql_type) && !options[:primary_key]
    sql << " NULL" unless options[:null] == false || options_include_default?(options)
  end
  if charset = options[:charset]
    sql << " CHARACTER SET #{charset}"
  end
  if collation = options[:collation]
    sql << " COLLATE #{collation}"
  end
  if as = options[:as]
    sql << " AS (#{as})"
    if options[:stored]
      sql << (mariadb? ? " PERSISTENT" : " STORED")
    end
  end
  add_sql_comment!(super, options[:comment])
end