title: Unity build and Run game error: Error building Player: Extracting referenced dlls failed
body: <p>Previously created a game with Unity engine 4.5 now updated to unity engine 5. Game run well and is working perfecting however when I click build and run for android I got the following error:<br>
  As a beginner I don't know what to do with this error</p>
  
  <pre><code>NullReferenceException: Object reference not set to an instance of an object
      UnityEditor.PluginImporter+&lt;GetImporters&gt;c__AnonStoreyC.&lt;&gt;m__E (UnityEditor.PluginImporter imp) (at C:/buildslave/unity/build/artifacts/generated/common/editor/PluginImporterBindings.gen.cs:104)
      System.Linq.Enumerable+&lt;CreateWhereIterator&gt;c__Iterator1D`1[UnityEditor.PluginImporter].MoveNext ()
      System.Collections.Generic.List`1[UnityEditor.PluginImporter].AddEnumerable (IEnumerable`1 enumerable) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Collections.Generic/List.cs:128)
      System.Collections.Generic.List`1[UnityEditor.PluginImporter]..ctor (IEnumerable`1 collection) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Collections.Generic/List.cs:65)
      System.Linq.Enumerable.ToArray[PluginImporter] (IEnumerable`1 source)
      UnityEditor.PluginImporter.GetImporters (System.String platformName) (at C:/buildslave/unity/build/artifacts/generated/common/editor/PluginImporterBindings.gen.cs:103)
      UnityEditor.PluginImporter.GetImporters (BuildTarget platform) (at C:/buildslave/unity/build/artifacts/generated/common/editor/PluginImporterBindings.gen.cs:111)
      UnityEditor.AndroidPluginImporterExtension.CheckFileCollisions (System.String buildTargetName)
      UnityEditorInternal.PluginsHelper.CheckFileCollisions (BuildTarget buildTarget) (at C:/buildslave/unity/build/Editor/Mono/Plugins/PluginsHelper.cs:25)
      UnityEditor.BuildPlayerWindow:BuildPlayerAndRun()
  </code></pre>