unity package manager ui 报错An ite m with the same key has alrea d ybeen added.Key

class="superseo">unity 在manifest.json 添加了 “com.unity.package-manager-ui”: “2.0.7”,
在unity 界面window下，还是没有Package Manager，
我的报错：
An ite m with the same key has alrea d ybeen added.Key: System.Buffers.dll

解决办法：
删除多余的System.Buffers.dll即可