I am getting this error when doing the lighting build on a very large landscape, no added foliage or other meshes yet, just the plain landscape with materials added to it. Not sure how to correct his.
Error === Lightmass crashed: ===
Assertion failed: NumMaterialElements > 0 [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.8\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingMesh.cpp] [Line: 108]
KERNELBASE.dll {0x00007ffb2285ec58} + 0 bytes
UnrealLightmass-Core.dll {0x00007ffb0219edbf} + 0 bytes
UnrealLightmass-Core.dll {0x00007ffb02081738} + 0 bytes
UnrealLightmass-Core.dll {0x00007ffb02062778} + 0 bytes
UnrealLightmass.exe!Lightmass::FStaticLightingMesh::Import() {0x00007ff69a1b7983} + 0 bytes
UnrealLightmass.exe!Lightmass::FLandscapeStaticLightingMesh::Import() {0x00007ff69a1b4ca5} + 0 bytes
UnrealLightmass.exe!Lightmass::FLightmassImporter::ImportObjectArray > >() {0x00007ff69a14fc63} + 0 bytes
UnrealLightmass.exe!Lightmass::FScene::Import() {0x00007ff69a1b65ec} + 0 bytes
UnrealLightmass.exe!Lightmass::FLightmassImporter::ImportScene() {0x00007ff69a1b82d0} + 0 bytes
UnrealLightmass.exe!Lightmass::BuildStaticLighting() {0x00007ff69a18299f} + 0 bytes
UnrealLightmass.exe!Lightmass::LightmassMain() {0x00007ff69a1bf3b8} + 0 bytes
UnrealLightmass.exe!main() {0x00007ff69a1dd94f} + 0 bytes
UnrealLightmass.exe!__tmainCRTStartup() {0x00007ff69a23950b} + 0 bytes
KERNEL32.DLL {0x00007ffb24c23b52} + 0 bytes
ntdll.dll {0x00007ffb266ea6f4} + 0 bytes
ntdll.dll {0x00007ffb266ea6f4} + 0 bytes
[File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.8\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingMesh.cpp] [Line: 108]