technoweenie/serialized_attributes — comment on commit c5d4f5961cf031952515f38e36128f15730c9fe3
File:  line 0
By technoweenie:

These aren't stored in a db column. The serialized attributes are stored as a json hash essentially. Ideally nil values wouldn't get written in the hash before being serialized so you don't have a bunch of extra false/nil keys.