Can't replace/remove a has_one related object

All,

I have two models, Job and Document.

Job has_one :document

I perform this:

@current_job.document.destroy

which successfully removes all the appopriate DB records.

However, if I attempt to do:

@current_job.document = nil

OR

@current_job.build_document(…)

I get a TypeError: can’t modify frozen hash exception.

Why can’t I reassign nil to the associated document for my job?

Thanks,
Wes

OK, I see now that the destroy instance method says that it “freezes
this instance to reflect that no changes should be made (since they
can‘t be persisted).”

Fine. I don’t want to work with that instance any more.

Why can’t I reassign to the has_one relationship?

Wes