NoMethodError: undefined method 'to_sym' for CustomStrategy

Description

After upgrading from Version 6.2.0 to 6.2.1 our custom strategy was broken.
-> NoMethodError: undefined method 'to_sym' for CustomStrategy

This commit broke our code https://github.com/thoughtbot/factory_bot/commit/1b81d5dc258e5f1ad25c5109cb4bf3f6be83deb4

The change is not mentioned in the NEWS.rb nor in the GETTING_STARTED.md

https://www.rubydoc.info/gems/factory_bot/file/GETTING_STARTED.md#custom-strategies

Solution

If someone comes here with the same Problem it is super easy to fix. Just add the to_sym to your strategy. :)

Question

Could someone explain to me or point me in the direction where I can find more information why the custom strategies should be defined like this and not like the one underneath. There is no problem i'm just curious.

class JsonStrategy
  def initialize
    @strategy = FactoryBot.strategy_by_name(:create).new
  end

  delegate :association, to: :@strategy

  def result(evaluation)
    @strategy.result(evaluation).to_json
  end

  def to_sym
    :json
  end
end

class JsonStrategy < FactoryBot::Strategy::Create
  def result(evaluation)
    super.to_json
  end

  def to_sym
    :json
  end
end

Read commit 1b81d5dc258e5f1ad25c5109cb4bf3f6be83deb4, then compare its behavior with the custom strategies section in GETTING_STARTED.md and the entries in NEWS.rb. Done means the custom-strategy interface and the difference between the two examples are clearly documented, including the 6.2.1 breaking change.