背景：
近期公司一同事发布一组件YHCommonSDK新版本到github,
然后本地执行pod search YHCommonSDK 或者 pod install，就出现问题了。
问题：
ArgumentError - comparison of Pod::Version with nil failed
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/aggregate.rb:60:in `<'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/aggregate.rb:60:in `block in representative_set'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/aggregate.rb:56:in `each'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/aggregate.rb:56:in `representative_set'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/manager.rb:129:in `block in search_by_name'
/Users/zxl/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/set.rb:324:in `each_key'
/Users/zxl/.rvm/rubies/ruby-2.4.1/lib/ruby/2.4.0/set.rb:324:in `each'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/manager.rb:128:in `map'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.6.0.beta.2/lib/cocoapods-core/source/manager.rb:128:in `search_by_name'
/Users/zxl/.rvm/gems/ruby-2.4.1@global/gems/cocoapods-search-1.0.0/lib/cocoapods-search/command/search.rb:87:in `local_search'
/Users/zxl/.rvm/gems/ruby-2.4.1@global/gems/cocoapods-search-1.0.0/lib/cocoapods-search/command/search.rb:63:in `run'
/Users/zxl/.rvm/gems/ruby-2.4.1@global/gems/claide-1.0.2/lib/claide/command.rb:334:in `run'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-1.6.0.beta.2/lib/cocoapods/command.rb:52:in `run'
/Users/zxl/.rvm/gems/ruby-2.4.1/gems/cocoapods-1.6.0.beta.2/bin/pod:55:in `<top (required)>'
/Users/zxl/.rvm/gems/ruby-2.4.1/bin/pod:23:in `load'
/Users/zxl/.rvm/gems/ruby-2.4.1/bin/pod:23:in `<main>'
/Users/zxl/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in `eval'
/Users/zxl/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in `<main>'
原因：
公司内部对YHCommonSDK 有2个版本，一个对外发布，一个对公司内部发布。
之前公司把内部的YHCommonSDK 的本地仓库给删除掉了，因此本地仓库得下来的YHCommonSDK仓库只是一个空的文件夹。
就是这时候如果执行 pod search 或者 pod install的时候
cocoapods搜索 YHCommonSDK 是会搜索 本地私有仓库 跟 github的master仓库
但是因为本地仓库只剩下一个空文件夹，所以便报错:
ArgumentError - comparison of Pod::Version with nil failed
解决：
删除本地仓库YHCommonSDK的文件夹就可以了，
与cocoapods版本、ruby版本都无关系。
