```
Hash.new.method(:deep_merge!).source_location
 => ["/home/ahorek/.rvm/gems/jruby-head/gems/activesupport-6.1.1/lib/active_support/core_ext/hash/deep_merge.rb", 23]

Concurrent::Hash.new.method(:deep_merge!).source_location
NameError (undefined method `deep_merge!' for class `Concurrent::Hash')
```