Right click the folder New Folder in the attached project and select Export Package.
In the Export Package window, click on the name of any asset and you get the following error:

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.TreeView.HandleUnusedMouseEventsForNode (Rect rect, UnityEditor.TreeViewItem item, Boolean firstItem) (at C:/buildslave/unity/build/Editor/Mono/GUI/TreeView/TreeView.cs:299)
UnityEditor.TreeView.DoItemGUI (UnityEditor.TreeViewItem item, Int32 row, Single rowWidth, Boolean hasFocus) (at C:/buildslave/unity/build/Editor/Mono/GUI/TreeView/TreeView.cs:444)
UnityEditor.TreeView.IterateVisibleItems (Int32 firstRow, Int32 numVisibleRows, Single rowWidth, Boolean hasFocus) (at C:/buildslave/unity/build/Editor/Mono/GUI/TreeView/TreeView.cs:568)
UnityEditor.TreeView.OnGUI (Rect rect, Int32 keyboardControlID) (at C:/buildslave/unity/build/Editor/Mono/GUI/TreeView/TreeView.cs:504)
UnityEditor.PackageExportTreeView.OnGUI (Rect rect) (at C:/buildslave/unity/build/Editor/Mono/GUI/PackageExportTreeView.cs:147)
UnityEditor.PackageExport.TreeViewArea (Boolean showLoadingScreen) (at C:/buildslave/unity/build/Editor/Mono/GUI/PackageExport.cs:211)
UnityEditor.PackageExport.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/GUI/PackageExport.cs:132)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:187)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:180)
UnityEditor.HostView.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:76)

After that selecting any other asset in that window will not work. The workaround is to close and reopen the Package Export window

This is a regression from 5.3.0b3 (b6181bece87a)