InvalidOperationException error is thrown after CinemachineImpulseChannels asset is created.

Steps to repro:
1. Create a new project.
2. Window > Package Manager > Cinemachine(2.6.0-preview.5) > Install.
3. Cinemachine menu > Virtual Camera > Extension > Add Extension > CinemachineImpulseListner.
4. In Cinemachine Impulse Listner > Edit > Save/Cancel.

Actual Result:
InvalidOperationException error is thrown in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a13, 2020.2.0a12, 2020.1.0b11, 2020.1.0b10 with Package version 2.6.0-preview.5, 2.5.0.

Working Fine in:
2020.2.0a11, 2020.1.0b9 with Package version 2.6.0-preview.5

Environment:
Occurring only on Windows 10.

Stacktrace:
InvalidOperationException: Stack empty.
System.Collections.Generic.Stack`1[T].ThrowForEmptyStack () (at <525dc68fbe6640f483d9939a51075a29>:0)
System.Collections.Generic.Stack`1[T].Pop () (at <525dc68fbe6640f483d9939a51075a29>:0)
UnityEditor.PropertyDrawer.OnGUISafe (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
UnityEditor.PropertyHandler.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.Rect visibleArea) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
UnityEditor.PropertyHandler.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
UnityEditor.PropertyHandler.OnGUILayout (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.GUILayoutOption[] options) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
UnityEditor.EditorGUILayout.PropertyField (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.GUILayoutOption[] options) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
UnityEditor.EditorGUILayout.PropertyField (UnityEditor.SerializedProperty property, System.Boolean includeChildren, UnityEngine.GUILayoutOption[] options) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
UnityEditor.Editor.DrawPropertiesExcluding (UnityEditor.SerializedObject obj, System.String[] propertyToExclude) (at <d302ee0b7fcd4d8184c0fe84f62c3cc1>:0)
Cinemachine.Editor.BaseEditor`1[T].DrawRemainingPropertiesInInspector () (at library/packagecache/com.unity.cinemachine@2.6.0-preview.3/editor/utility/baseeditor.cs:81)
Cinemachine.Editor.CinemachineImpulseListenerEditor.OnInspectorGUI () (at library/packagecache/com.unity.cinemachine@2.6.0-preview.3/editor/impulse/cinemachineimpulselistenereditor.cs:15)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <23f880b0551248cb8ca27306bc291abd>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)