Steps to repro:

1. Open attached project and 't1' scene;
2. Select 'Terrain' gameobject in the Hierarchy;
3. Go to 'Place Trees' tab;
4. In the Terrain Inspector click on the 'Missing' tree prefab.

Expected result:
Prefab is selected and Editor doesn't crash.

Actual result:
Editor crashes. See attached video.

Last calls from the stacktrace:
0x00000000621C3C15 (Mono JIT Code) (wrapper managed-to-native) UnityEditor.GameObjectUtility:GetStaticEditorFlags (UnityEngine.GameObject)
0x0000000000C7D48C (Mono JIT Code) [C:\buildslave\unity\build\Editor\Mono\TerrainEditor\TerrainInspector.cs:1074] UnityEditor.TerrainInspector:ShowTrees ()
0x00000000621E86B8 (Mono JIT Code) [C:\buildslave\unity\build\Editor\Mono\TerrainEditor\TerrainInspector.cs:1596] UnityEditor.TerrainInspector:OnInspectorGUI ()
0x000000006213D5D7 (Mono JIT Code) [C:\buildslave\unity\build\Editor\Mono\Inspector\InspectorWindow.cs:1245] UnityEditor.InspectorWindow:DrawEditor (UnityEditor.Editor[],int,bool,bool&,UnityEngine.Rect&)
0x000000006210A796 (Mono JIT Code) [C:\buildslave\unity\build\Editor\Mono\Inspector\InspectorWindow.cs:1022] UnityEditor.InspectorWindow:DrawEditors (UnityEditor.Editor[])
0x0000000062107725 (Mono JIT Code) [C:\buildslave\unity\build\Editor\Mono\Inspector\InspectorWindow.cs:361] UnityEditor.InspectorWindow:OnGUI ()

Regression introduced in Unity 2017.3.0b1.

Notes:
- Reproduces in 2018.1.0a6, 2017.3.0b11, 2017.3.0b1;
- Not reproduces in 2017.3.0a6, 2017.2.0p3;
- Reproduces on both Windows 10 and OSX 10.13.1.