Save a boolean as null - ruby-on-rails

Question

dp1 has three possible states true, false, and null. I would like to save dp1 as null. This is correctly done according to the logs, but it is saved as true while there is no default value in my db.
Started PATCH "/equipments/2" for 127.0.0.1 at 2018-08-01 11:49:23 +0200
Processing by EquipmentsController#update as JS
Parameters: {"utf8"=>"✓", "equipment"=>{"title"=>"TV ", "dp1"=>"nil"}, "commit"=>"Save", "id"=>"2"}
Equipment Load (0.1ms) SELECT "equipment".* FROM "equipment" WHERE "equipment"."id" = ? LIMIT ? [["id", 2], ["LIMIT", 1]]
↳ app/controllers/equipments_controller.rb:124
User Load (0.3ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? ORDER BY "users"."id" ASC LIMIT ? [["id", 3], ["LIMIT", 1]]
↳ /Users/Mesnet/.rvm/gems/ruby-2.5.1/gems/orm_adapter-0.5.0/lib/orm_adapter/adapters/active_record.rb:17
(0.0ms) begin transaction
↳ app/controllers/equipments_controller.rb:81
Equipment Update (0.4ms) UPDATE "equipment" SET "dp1" = ?, "updated_at" = ? WHERE "equipment"."id" = ? [["dp1", 1], ["updated_at", "2018-08-01 09:49:23.413563"], ["id", 2]]
↳ app/controllers/equipments_controller.rb:81
(0.7ms) commit transaction
↳ app/controllers/equipments_controller.rb:81
Rendering equipments/js/create.js.erb
Rendered equipments/js/create.js.erb (0.4ms)
Completed 200 OK in 31ms (Views: 26.0ms | ActiveRecord: 1.5ms)
How can I force my value to be saved as null if the form is null?

Answer 1

Only empty strings or nil value are coerced to nil. Please check the boolean type documentation for active record.
You will have to check for 'nil' string and convert it to empty string or nil value at controller level. Something like this:
def update
.....
data = params.require(: equipment).permit(:title, :dp1).to_h
data[:dp1] = '' if data[:dp1] == 'nil'
.....
end