"Assertion failed on expression" exception thrown on creating a prefab of GameObject with child override whose prefab instance is missing

Steps to reproduce:
1) Create new project
2) Create an empty GameObject prefab A
3) Add an empty child GameObject to A > Apply to prefab A
4) Delete prefab A from project
5) Press hotkey "Ctrl+Z" and hierarchy shows override option for child gameObject.
6) Drag gameObject A to hierarchy and in dialogue box, click button "original prefab".

Actual result: "Assertion failed on expression" exception is thrown

Expected result: No exception is thrown.

Occurring with: 2018.3.0f2, 2018.3.0f1

Working fine in: 2019.1.0a11, 2018.3.0b12

Environment: Windows and Mac

Stack trace:
Assertion failed on expression: 'originalRootGameObjectPrefab != NULL'
UnityEditorInternal.InternalEditorUtility:ProjectWindowDrag()
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)