ActionView::Helpers::FormBuilder attribute parent_builder disappeared in rails 4.2?

Hi there,

I’m trying to update a ruby on rails app from 4.2 to 5.0 version.

I noticed that in rails previous versions the attribute parent_builder existed in the api (http://www.rubydoc.info/docs/rails/3.2.8/ActionView/Helpers/FormBuilder).

However in more recent rails versions it no longer exits…(http://api.rubyonrails.org/v4.0.0/classes/ActionView/Helpers/FormBuilder.html).

What is the meaning/utility of this parent_builder attribute and how can I replace it to more recent rails versions?

Thank you in advance,

João Bordalo