has_one through的目标类配置可能会导致错误

[moioo]

class Post < ApplicationRecord
  second_level_cache
  belongs_to :topic, touch: true
end

class Hotspot < ApplicationRecord
	belongs_to :post, required: false
	has_one :topic, through: :post
end


#test
    hotspot = Hotspot.create(summary: 'summary')#
    assert_equal hotspot.persisted?, true
    assert_nil hotspot.topic
#error
NoMethodError: undefined method `klass' for nil:NilClass
active_record/has_one_association.rb:14:in `find_target'

如果Post的topic的配置require: true，而在Hotspot中post的配置为require: false时，如果创建Hotspot时post为空 has_one就会报错