How to reproduce:
1. Open the attached project
2. Enter the Play mode

Expected result: Editor does not crash.
Actual result: Editor crashes.

Reproducible with - 2018.2.0a1, 2018.2.0b11, 2018.3.0a1, 2018.3.0a4
Not reproducible with - 2017.1.4p2, 2017.2.3p1, 2017.4.6f1, 2018.1.0a1, 2018.1.7f1

Stack trace:
(Unity) FindRelativeTransformWithPath
(Unity) Transform_CUSTOM_FindRelativeTransformWithPath
(Mono JIT Code) (wrapper managed-to-native) UnityEngine.Transform:FindRelativeTransformWithPath (UnityEngine.Transform,string,bool)
(Mono JIT Code) [C:\buildslave\unity\build\Runtime\Transform\ScriptBindings\Transform.bindings.cs:290] UnityEngine.Transform:Find (string)
(Mono JIT Code) [C:\Users\QA Students\Desktop\1056406\Assets\MyScript.cs:9] MyScript:Start ()
(Mono JIT Code) (wrapper runtime-invoke) object:runtime_invoke_void__this__ (object,intptr,intptr,intptr)
(mono) [c:\buildslave\mono\build\mono\mini\mini.c:4937] mono_jit_runtime_invoke
(mono) [c:\buildslave\mono\build\mono\metadata\object.c:2623] mono_runtime_invoke
(Unity) scripting_method_invoke
(Unity) ScriptingInvocation::Invoke
(Unity) MonoBehaviour::InvokeMethodOrCoroutineChecked
(Unity) MonoBehaviour::InvokeMethodOrCoroutineChecked
<...>

Fixed in 2018.3.0a6
Backported to 2018.2.3f1