When clear has been called, we might have other operations added to the association (typically a PUT) after that.

This is correctly supported in all the methods (size, get...) except for the getKeys() method.

It was not really an issue until now as we did not reuse the state of the Association but it is indeed a bug and in the way of OGM-1064 In Progress as we do now need to track the state of the Association.