[Nitro] Storing Og objects in ordinary instance variables

[itsme213]

Is it OK to do this? Any problems with storing Ruby object-refs instead of 
Og oids?

class A < Og::Entity
  # some props etc.
end

class B < Og::Entity
  # some props etc.
  def a= (a)
    @a = a
  end

  def a
    @a
  end
end

Thanks.