To reproduce:

1. Open the project, attached by the tester (blankSpriteMode.zip)
2. Import some kind of PNG image
3. Rename it "image"
4. Enter Play mode
5. Press Space
6. Select the image
7. Observe Sprite Mode in the import settings in the Inspector
8. (Optional) Observe the SwitchType.cs script

Expected: changing import settings of an image from Default to Sprite via script automatically changes Sprite Mode to Single
Actual: Sprite Mode is blank after switching import settings from Default to Sprite via script

Reproduced in 5.5.2p1, 5.6.1f1, 2017.1.0b10, 2017.2.0a4
Did not reproduce in 5.5.1f1, 5.5.2f1
Regressions introduced in 5.5.2p1

Fixed in 2017.3.0a1