How to reproduce:
1. Open the attached project "BehaviorDesigner.zip"
2. Observe the crash

Reproduced with: 2018.1.0b5, 2018.1.0b9, 2018.2.0a2
Not reproducible with: 2017.2.1p4, 2017.3.1p2, 2018.1.0b4

Notes:
- Crash is not reproducible with .NET 3.5
- Assets/BehaviorDesignerEditor.dll is the culprit
- Error thrown when .NET 4.6 is enabled: Assertion failed on expression: 'exception != SCRIPTING_NULL'

========== OUTPUTTING STACK TRACE ==================

0x0000000140BD7A5C (Unity) scripting_stack_trace_info_for
0x0000000140BC7593 (Unity) Scripting::LogException
0x0000000140BD6C3A (Unity) scripting_class_get_methods
0x0000000140BAAADC (Unity) PopulateMethods
0x0000000140BA33EB (Unity) CreateMonoScriptCache
0x0000000140BA5171 (Unity) FindOrCreateMonoScriptCache
0x0000000140BAD79D (Unity) MonoScript::Renew
0x0000000140BAC4D4 (Unity) RebuildAllScriptCaches
0x0000000140BA387C (Unity) MonoManager::EndReloadAssembly
0x0000000140BAD48D (Unity) MonoManager::ReloadAssembly
0x0000000140E4EBBF (Unity) LoadDomainAndUserAssemblies
0x0000000140E4EFF8 (Unity) LoadMonoAssembliesAndRecompileIfNecessary
0x00000001413AEFE7 (Unity) Application::InitializeProject
0x00000001415A9E31 (Unity) WinMain
0x000000014272BB37 (Unity) __scrt_common_main_seh
0x00007FFB53661FE4 (KERNEL32) BaseThreadInitThunk
0x00007FFB538BEFB1 (ntdll) RtlUserThreadStart

========== END OF STACKTRACE ===========

Fixed in: 2018.2.0a3 (a0fbd73019b1)