Parent is result of to_params on an instance of a has_many

This behavior seems incorrect in the case where belongs_to has not been set.

The parent is inserted by the fetch method of has_many_association (https://github.com/remiprev/her/blob/master/lib/her/model/associations/has_many_association.rb#L88)

I believe that the to_params method (https://github.com/remiprev/her/blob/master/lib/her/model/parse.rb#L34) should be responsible for removing the parent for the hash. 

However, the class, Foo::Bar in my example, does not know its parent, Foo::User, and therefore can't tell if it should delete :user from the hash. To remedy this I'm leaning towards adding a class variable that tracks which params need to be removed by to_params. Does this sound reasonable or do you believe there is a preferable method?