title: Yarn can't add dependency via git+ssh because package doesn't have a "_uid"
body: <p>We have a dependency that lives on private GitLab instance, but we can't get yarn to add it.</p>
  
  <p>Installing the package like this:</p>
  
  <p><code>yarn add git+ssh://git@privateserver.org:team/package-name.git</code></p>
  
  <p>results in this error:</p>
  
  <p><code>error Package "package-name@0.9.2" doesn't have a "_uid".</code></p>
  
  <p>I'm thinking this is yarn-specific because using npm does work ... e.g. this command successfully installs the package:</p>
  
  <p><code>npm install --save git+ssh://git@privateserver.org:team/package-name.git</code></p>
  
  <p>I've looked through yarn's documentation and gone through pages of google results, but can't really find any information the <code>_uid</code>. Anyone have any ideas what's going on here?</p>