class ActiveModel::LazyAttributeSet

def default_attribute(
  name,
  value_present = true,
  value = values.fetch(name) { value_present = false }
)
  type = additional_types.fetch(name, types[name])
  if value_present
    @attributes[name] = Attribute.from_database(name, value, type, @casted_values[name])
  elsif types.key?(name)
    if attr = default_attributes[name]
      @attributes[name] = attr.dup
    else
      @attributes[name] = Attribute.uninitialized(name, type)
    end
  else
    Attribute.null(name)
  end
end