TypeError: can't quote RGeo::Cartesian::PolygonImpl

[Adam TTN]

This is my gemfile rails & rgeo setup:

gem 'rails', '~> 5.2.0'
gem 'mysql2', '~> 0.5.2'
...
gem 'rgeo', '1.0.0'

gem 'rgeo-activerecord', '~> 6.0.0'

gem 'activerecord-mysql2rgeo-adapter', '2.2.0'

This is how table has been created:

class Create Zones < ActiveRecord::Migration[5.2]

  def change

    create_table :zones do |t|

      t.string  :name,        null: false

      t.integer :external_id

      t.polygon :internal_polygon

    end

  end

end

I have sth like this in schema.rb:

# Could not dump table "zones" because of following NameError

#   uninitialized constant ActiveRecord::ConnectionAdapters::Mysql2RgeoAdapter::INDEX_TYPES

This is what I'm trying to create and save data:

z = Zone.new
z.internal_polygon = RGeo::Cartesian.factory(:srid => 4326).parse_wkt("POLYGON((10 10,20 10,20 20,10 20,10 10))")
z.valid? # true
z.save # TypeError: can't quote RGeo::Cartesian::PolygonImpl from (irb):16

What can I do with that?