Ruby Win32注册表：系统在查找不带'；不存在

我正在编写一个ruby函数，从给定的DisplayName获取卸载字符串。我的函数只有在我给它一个要查找的现有DisplayName时才能成功运行，当我给它一个不存在的东西时它就会崩溃。我不确定在什么条件下检查哪个变量（nil？empty？），这样我就可以向脚本抛出一个异常，打印一条消息“notfound”，而不是崩溃

require 'win32/registry'

def get_uninstallstring(app_name)

  paths = [ "Software\\Microsoft\\Windows\\CurrentVersion\\Uninstall",
            "Software\\Wow6432Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall",
            "Software\\Wow6464Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall"  ]
  access_type = Win32::Registry::KEY_ALL_ACCESS

  paths.each do |path|         # This is line 9
    Win32::Registry::HKEY_LOCAL_MACHINE.open(path, access_type) do |reg|
      reg.each_key do |key|
        k = reg.open(key) 
        app = k['DisplayName'] rescue nil
        if app == app_name
          str = k['UninstallString'] rescue nil
          return str
        end
      end
    end
  end
  return false
end

puts get_uninstallstring("ABC")    # This is line 24

以下是错误输出：

C:/ruby/1.9.1/win32/registry.rb:385:in `open': The system cannot find the file specified. (Win32::Registry::Error)
        from C:/heliopolis/opscode/chef/embedded/lib/ruby/1.9.1/win32/registry.rb:496:in `open'
        from test.rb:10:in `block in get_uninstallstring'
        from test.rb:9:in `each'
        from test.rb:9:in `get_uninstallstring'
        from test.rb:24:in `<main>'

C:/ruby/1.9.1/win32/registry.rb:385:在“打开”中：系统找不到指定的文件。（Win32:：注册表：：错误）
来自C:/heliopolis/opscode/chef/embedded/lib/ruby/1.9.1/win32/registry.rb:496:in'open'
from test.rb:10:in'block in get_uninstallstring'
来自测试。rb:9:in'each'
来自test.rb:9:in'get\u uninstallstring'
来自测试。rb:24:in`'

所以我自己找到了一个解决方案。我必须编写另一个函数来检查键是否存在于给定的路径中，然后才能实际获取其值

def key_exists?(path)
  begin
    Win32::Registry::HKEY_LOCAL_MACHINE.open(path, ::Win32::Registry::KEY_READ)
    return true
  rescue
    return false
  end
end

下面是修改后的get函数：

  paths.each do |path| 
    if key_exists?(path)
      Win32::Registry::HKEY_LOCAL_MACHINE.open(path, access_type) do |reg|
        reg.each_key do |key|
          k = reg.open(key)
          app = k['DisplayName'] rescue nil
          if app == app_name
        return k['UninstallString'] rescue nil
          end
        end
      end
    else
      return false
    end
  end