Steps to repro:

1. Open attached project and 't1' scene;
2. Select 'Terrain' gameobject in the Hierarchy;
3. In the Terrain Inspector go to 'Place Tree' tab;
4. In the Hierarchy click on 'Directional Light' gameobject;
5. In the Hierarchy click on 'Main Camera' gameobject.

Expected result:
Gameobject is selected.

Actual result:
Editor crashes. See attached video. Last calls from stacktrace:

#0 0x0000010093f6f0 in GameObject::QueryComponentByType(Unity::Type const*) const
#1 0x00000100a1cedf in Projector::SetupProjectorSettings(Material*, ProjectorRenderSettings&)
#2 0x00000100a1eff5 in Projector::PrepareRenderNode(unsigned int, unsigned int, Projector*, RenderNodeQueue&, PerThreadPageAllocator&)
#3 0x00000100a4a80d in EndRenderQueueExtraction(RenderNodeQueuePrepareContext*)
#4 0x000001009a5555 in CullResults::GetOrCreateSharedRendererScene()
#5 0x000001015467f3 in Camera::RenderEditorCamera(Camera::EditorDrawingMode, DrawGridParameters const*, CullResults*, Camera::RenderFlag, int)

Regression introduced in Unity 2017.3.0f2.

Notes:
- Reproducible in 2018.1.0a7, 2018.1.0a6, 2017.3.0f2;
- Not reproducible in 2018.1.0a5, 2017.3.0f1, 2017.2.0p4, 2017.1.2p4;
- Reproducible on both Windows 10 and macOSX 10.13.1;
- Reproducible only when Terrain with missed prefab is selected in the Inspector;
- The case might not repro for the first time, if it doesn't, select Terrain (with opened Place Tree tab having missed prefab), click on Camera and Directional Light or vice versa. Repeat several times.

Fixed in: 5.6.5p1, 2017.1.3p1, 2017.2.1p3, 2017.3.0p2, 2017.4.0f1, 2018.1.0b3, 2018.2.0a1