Steps to repro:

1. Open attached project;
2. In the Project folder multiselect four .spm prefabs by shift-clicking on them;
3. In the Inspector double-click on any Speedtree preview.

Expected result:
No errors are thrown.

Actual result:

Multiple errors:
'AssetImporterEditor: assetEditor has null targets!
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)'

are thrown in the console. See attached video.

Regression introduced in Unity 2017.2.0b1.

Notes:
- Reproducible in Unity 2017.3.0a4, 2017.2.0b7, 2017.2.0b1;
- Not reproducible in 2017.2.0a4, 2017.1.0p3, 5.6.1p2;
- Reproducible on Windows 10 and on OSX 10.12.5;
- Reproducible only when multi-selecting speedtree prefabs; not reproducible when multi-selecting other prefabs.