Ruby - 2.3.2 ビルドインストール時のエラー！

/home/foo/ruby-2.3.2/lib/rubygems/installer.rb:233:in `check_executable_overwrite': no implicit conversion of nil into String (TypeError)
        from /home/foo/ruby-2.3.2/lib/rubygems/installer.rb:474:in `block in generate_bin'
        from /home/foo/ruby-2.3.2/lib/rubygems/installer.rb:461:in `each'
        from /home/foo/ruby-2.3.2/lib/rubygems/installer.rb:461:in `generate_bin'
        from /home/foo/ruby-2.3.2/lib/rubygems/installer.rb:301:in `install'
        from ./tool/rbinstall.rb:686:in `call'
        from ./tool/rbinstall.rb:686:in `block in <class:Installer>'
        from ./tool/rbinstall.rb:754:in `block (2 levels) in <main>'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:821:in `block in each_spec'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:743:in `block (2 levels) in each_gemspec'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:742:in `each'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:742:in `block in each_gemspec'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:741:in `each'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:741:in `each_gemspec'
        from /home/foo/ruby-2.3.2/lib/rubygems/specification.rb:819:in `each_spec'
        from ./tool/rbinstall.rb:751:in `block in <main>'
        from ./tool/rbinstall.rb:801:in `block in <main>'
        from ./tool/rbinstall.rb:798:in `each'
        from ./tool/rbinstall.rb:798:in `<main>'
uncommon.mk:260: recipe for target 'do-install-all' failed
make: *** [do-install-all] Error 1

  def check_executable_overwrite filename # :nodoc:
    return if @force

    generated_bin = File.join @bin_dir, formatted_program_filename(filename)

    return unless File.exist? generated_bin

    ruby_executable = false
    existing = nil

    open generated_bin, 'rb' do |io|
      next unless io.gets =~ /^#!/ # shebang
      io.gets # blankline

      # TODO detect a specially formatted comment instead of trying
      # to run a regexp against Ruby code.
      next unless io.gets =~ /This file was generated by RubyGems/

      ruby_executable = true
      existing = io.read.slice(%r{
          ^(
            gem \s |
            load \s Gem\.bin_path\(
          )
          (['"])(.*?)(\2),
        }x, 3)
    end

    return if spec.name == existing

    # somebody has written to RubyGems' directory, overwrite, too bad
    return if Gem.default_bindir != @bin_dir and not ruby_executable

    question = "#{spec.name}'s executable \"#{filename}\" conflicts with ".dup

    if ruby_executable then
      question << existing

      return if ask_yes_no "#{question}\nOverwrite the executable?", false

      conflict = "installed executable from #{existing}"
    else
      question << generated_bin

      return if ask_yes_no "#{question}\nOverwrite the executable?", false

      conflict = generated_bin
    end

    raise Gem::InstallError,
      "\"#{filename}\" from #{spec.name} conflicts with #{conflict}"
  end

@@ -230,7 +230,7 @@
     question = "#{spec.name}'s executable \"#{filename}\" conflicts with ".dup

     if ruby_executable then
-      question << existing
+      question << (existing || 'an unknown executable')

       return if ask_yes_no "#{question}\nOverwrite the executable?", false