Can't persist array in a Postgres column using Active Record

I know this question may sound duplicated, but none of the solutions I've found actually solved my problem.

I have a model named pet with photos column, here's my schema:

t.string "photos", default: [], array: true

I'm not using the serialize method in my class because a lot of other sources confirmed that it's not necessary.

Here's my object:

#<Pet id: 9, name: nil, age: nil, vaccinated: nil, male: nil, pet_description: nil, additional_info: nil, size: nil, neutered: nil, classified_id: nil, created_at: "2016-10-21 23:36:37", updated_at: "2016-10-21 23:55:50", kind: nil, photos: []>

No matter I do, I cannot persist a new photo array:

UPDATE "pets" SET "updated_at" = $1, "photos" = $2 WHERE "pets"."id" = $3  [["updated_at", 2016-10-21 23:51:30 UTC], ["photos", "{}"], ["id", 9]]

I've already tried several ways of persisting, like:

model.array << element
model.array_will_change!
model.save!  

or even (like this guy suggested, and this other guy as well):

update_attributes locations: locations + [ place ]

and none of them seems to work.

Using Postgres command line I was able to save and update and array with no problems, but this issue seems to be related to active record.

activerecord (5.0.0.1) postgres (9.6.0.0)

Thanks a lot :-)