Derived var reset to null when a var is redefined

Just ran into an issue below. When a variable defined in one cell is redefined again in another cell (e.g., due to a user error) , an object derived from the original variable is reset to null. Is this a problem in JJava or the underlying JShell? 

<img width="1077" alt="image" src="https://github.com/user-attachments/assets/2d6a1c06-d17d-44cc-acda-f04ef0a3cb32">

