module ActiveRecord::ConnectionAdapters::TimestampDefaultDeprecation

def emit_warning_if_null_unspecified(options)
  return if options.key?(:null)
  ActiveSupport::Deprecation.warn(<<-MSG.squish)
    `#timestamp` was called without specifying an option for `null`. In Rails 5,
    this behavior will change to `null: false`. You should manually specify
   `null: true` to prevent the behavior of your existing migrations from changing.
  MSG
end