```ruby
class AddDefaultConfigToApplication < ActiveRecord::Migration
  def change
    add_column :applications, :default_config, :jsonb, default: '{}'
    add_column :application_instances, :config, :jsonb, default: '{}'
  end
end
```

Set default config to hash instead of string
user
```ruby
class AddDefaultConfigToApplication < ActiveRecord::Migration
  def change
    add_column :applications, :default_config, :jsonb, default: {}
    add_column :application_instances, :config, :jsonb, default: {}
  end
end
```
assistant