Steps to reproduce:

1. Open Unity Editor;
2. Create new project and scene;
3. Add some files to project settings (could be either prefabs, models etc);
4. Drag any file that could be placed in SceneView from Project tab to the Scene view;
5. Observe the console.

Actual result:

NullReferenceException: (null)
UnityEditor.HandleUtility.CalcRayPlaceOffset (UnityEngine.Transform[] objects, Vector3 normal) (at /Users/builduser/buildslave/unity/build/artifacts/generated/common/editor/EditorHandlesUtilityBindings.gen.cs:700)
UnityEditor.GameObjectInspector.OnSceneDrag (UnityEditor.SceneView sceneView) (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/GameObjectInspector.cs:770)
UnityEditor.SceneView.CallEditorDragFunctions () (at /Users/builduser/buildslave/unity/build/Editor/Mono/SceneView/SceneView.cs:1790)
UnityEditor.SceneView.HandleDragging () (at /Users/builduser/buildslave/unity/build/Editor/Mono/SceneView/SceneView.cs:1803)
UnityEditor.SceneView.OnGUI () (at /Users/builduser/buildslave/unity/build/Editor/Mono/SceneView/SceneView.cs:1283)
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)

is shown in the console.
See attached actual.png screenshot and gif video.

Possible workaround is to drag object to the Hierarchy tab, in this case the error is not thrown.

Notes:
- Regression introduced in Unity 5.3.0b5;
- Reproduced on both OSX El Capitan 10.11 and Windows 7.