- Select all assets in the attached project
- Right click on the selection and choose Export Package
- Use Shift+Click to select the first few assets (example: http://i.imgur.com/dfoY13K.png)
- Click on the checkmark for the first item (Bomb_Small.fbx)
Notice the following error in the Console:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PackageExportTreeView.ItemWasToggled (UnityEditor.PackageExportTreeViewItem pitem) (at C:/buildslave/unity/build/Editor/Mono/GUI/PackageExportTreeView.cs:186)
UnityEditor.PackageExportTreeView+PackageExportTreeViewGUI.DoToggle (UnityEditor.PackageExportTreeViewItem pitem, Rect toggleRect) (at C:/buildslave/unity/build/Editor/Mono/GUI/PackageExportTreeView.cs:310)
UnityEditor.PackageExportTreeView+PackageExportTreeViewGUI.OnRowGUI (Rect rowRect, UnityEditor.TreeViewItem tvItem, Int32 row, Boolean selected, Boolean focused) (at C:/buildslave/unity/build/Editor/Mono/GUI/PackageExportTreeView.cs:270)
UnityEditor.TreeView.DoItemGUI (UnityEditor.TreeViewItem item, Int32 row, Single rowWidth, Boolean hasFocus) (at C:/buildslave/unity/build/Editor/Mono/GUI/TreeView/TreeView.cs:431)
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)

Deselecting multiple assets isn't working anymore because of this.

Regression from Unity 5.3.0b3 (b6181bece87a)