从 rails 5.1 迁移到 5.2 后，模型重新索引时会出现错误“TypeError：没有将 nil 隐式转换为 Hash”

Question

在我将 rails 从 5.1 升级到 5.2 并且Searchkick gem也升级到版本 4.3 之后，我尝试在我的模型上运行reindex ，但是对于测试和开发环境，每个模型都会出现错误。

TypeError: no implicit conversion of nil into Hash

来自（开发环境）的堆栈跟踪：

[1] pry(main)> Model.reindex
TypeError: no implicit conversion of nil into Hash
from /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/activesupport-5.2.4.2/lib/active_support/core_ext/hash/deep_merge.rb:24:in `merge!'

来自（测试环境）的堆栈跟踪：

TypeError:
  no implicit conversion of nil into Hash
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/activesupport-5.2.4.2/lib/active_support/core_ext/hash/deep_merge.rb:24:in `merge!'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/activesupport-5.2.4.2/lib/active_support/core_ext/hash/deep_merge.rb:24:in `deep_merge!'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/activesupport-5.2.4.2/lib/active_support/core_ext/hash/deep_merge.rb:19:in `deep_merge'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/searchkick-4.3.0/lib/searchkick/index_options.rb:287:in `index_options'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/searchkick-4.3.0/lib/searchkick/model.rb:65:in `searchkick_index_options'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/searchkick-4.3.0/lib/searchkick/index.rb:286:in `reindex_scope'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/searchkick-4.3.0/lib/searchkick/index.rb:201:in `reindex'
# /Users/vadymfilipov/.rvm/gems/ruby-2.5.5/gems/searchkick-4.3.0/lib/searchkick/model.rb:60:in `searchkick_reindex'
# ./lib/elastic.rb:9:in `map'
# ./lib/elastic.rb:9:in `reindex'