Weird rubygems error by redefining `find` method

broken_find.rb

module Enumerable
  undef find

  def find(ifnone=nil)
    return to_enum(:find, ifnone) unless block_given?

    each do |item|
      return item if yield item
    end
  end
end

Description.md

Here, with broken_find.rb required, specification.rb raises an error saying stub is an Array.

/Users/okuramasafumi/.rubies/ruby-2.6.1/lib/ruby/site_ruby/2.6.0/rubygems/specification.rb:1065:in find_active_stub_by_path': undefined method this' for #<Array:0x00007fc3e18ff960> (NoMethodError)

The error disappears with working_find.rb required.

The only difference is whether ifnone.call if ifnone exists or not.

However, in specification.rb uses find method without ifnone argument. This means ifnone is nil.

So, why adding ifnone.call if ifnone to broken_find.rb actually fixes the problem?

specification.rb

  # From rubygems
  
  def self.find_active_stub_by_path(path)
    stub = @@active_stub_with_requirable_file[path] ||= (stubs.find { |s|
      s.activated? and s.contains_requirable_file? path
    } || NOT_FOUND)
    stub.this
  end

working_find.rb

module Enumerable
  undef find

  def find(ifnone=nil)
    return to_enum(:find, ifnone) unless block_given?

    each do |item|
      return item if yield item
    end

    ifnone.call if ifnone
  end
end