class ActiveSupport::Cache::Entry

def convert_version_4beta1_entry!

to ensure that cache entries created under the old version still work with the new class definition.
The internals of this method changed between Rails 3.x and 4.0. This method provides the glue 
def convert_version_4beta1_entry!
  if defined?(@v)
    @value = @v
    remove_instance_variable(:@v)
  end
  if defined?(@c)
    @compressed = @c
    remove_instance_variable(:@c)
  end
  if defined?(@x) && @x
    @created_at ||= Time.now.to_f
    @expires_in = @x - @created_at
    remove_instance_variable(:@x)
  end
end