Null reference exception error occurs on maximizing test runner window

Steps to Repro:
1. Open attached or create a new project
2. Window > Test Runner
3. Dock the window > Maximize it

Actual Result:
1. Check the console for the errors

Working with:
2108.1.0a4, 2018.1.0a1, 2017.3.1p4,

Occurring with;
2018.2.0a7, 2018.1.0b13, 2018.1.0b1, 2018.1.0a7, 2018.1.0a6, 2018.1.0a5

Environment:
Only on Windows

Stack Trace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.TestTools.TestRunner.GUI.TestListGUIHelper.GetTheNearestCustomScriptAssembly () (at C:/buildslave/unity/build/Extensions/TestRunner/UnityEditor.TestRunner/GUI/Views/PlayModeTestListGUI.cs:80)
UnityEditor.TestTools.TestRunner.GUI.TestListGUIHelper.CanAddEditModeTestScriptAndItWillCompile () (at C:/buildslave/unity/build/Extensions/TestRunner/UnityEditor.TestRunner/GUI/Views/PlayModeTestListGUI.cs:48)
UnityEditor.TestTools.TestRunner.GUI.EditModeTestListGUI.RenderNoTestsInfo () (at C:/buildslave/unity/build/Extensions/TestRunner/UnityEditor.TestRunner/GUI/Views/EditModeTestListGUI.cs:27)
UnityEditor.TestTools.TestRunner.GUI.TestListGUI.RenderTestList () (at C:/buildslave/unity/build/Extensions/TestRunner/UnityEditor.TestRunner/GUI/Views/TestListGUIBase.cs:114)
UnityEditor.TestTools.TestRunner.TestRunnerWindow.OnGUI () (at C:/buildslave/unity/build/Extensions/TestRunner/UnityEditor.TestRunner/TestRunnerWindow.cs:179)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:291)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:284)
UnityEditor.HostView.InvokeOnGUI (Rect onGUIPosition) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:251)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)