title: Nuget doesn't install dependencies when 'targetFramework' attribute isn't specified
body: <p>According to the <a href="https://docs.nuget.org/create/nuspec-reference" rel="nofollow">nuspec reference</a> chapter "Specifying Dependencies in version 2.0 and above", it's possible to declare a <code>dependency</code> in a <code>group</code> element without an additional <code>targetFramework</code> attribute, which implies that this dependency is valid for all frameworks. So I went ahead an specified the following in a .nuspec for one of my packages:</p>
  
  <pre><code>&lt;dependencies&gt;
    &lt;group&gt;
      &lt;dependency id="DEPENDENCY" version="1.0.0" /&gt;
    &lt;/group&gt;
  
    &lt;group targetFramework="net40-client"&gt;
    &lt;/group&gt;
  
    &lt;group targetFramework="net45"&gt;
    &lt;/group&gt;
  &lt;/dependencies&gt;
  </code></pre>
  
  <p>After installing the package in one of my projects, the dependency isn't there at all. Neither in the project references nor in the <code>packages</code> folder in the root of my project. However when doing this:</p>
  
  <pre><code>&lt;dependencies&gt;
    &lt;group targetFramework="net40-client"&gt;
      &lt;dependency id="DEPENDENCY" version="1.0.0" /&gt;
    &lt;/group&gt;
  
    &lt;group targetFramework="net45"&gt;
      &lt;dependency id="DEPENDENCY" version="1.0.0" /&gt;
    &lt;/group&gt;
  &lt;/dependencies&gt;
  </code></pre>
  
  <p>... it works flawlessly. </p>
  
  <p>Is this a bug? ~~Do I possibly override the 'global' dependency configuration with the empty local declarations?~~ Or did I misunderstood something here?</p>
  
  <hr>
  
  <p><strong>EDIT</strong></p>
  
  <p>It's possible to declare empty dependency elements and still have 'a global one': <a href="https://github.com/dsplaisted/PCLStorage/blob/master/common/PCLStorage.nuspec" rel="nofollow">https://github.com/dsplaisted/PCLStorage/blob/master/common/PCLStorage.nuspec</a></p>