When using the AND node it will try to read both variables so the IsValid node becomes redundant. Use the IsValid Macro instead ( the one with ? ). You can also right click “ball” and select “Validated Get”.
Blueprint is not like C++ in this regard : both inputs to your AND node will be computed regardless of the value of the first pin, so, in any case, the Active property from the Ball object will be read, even if Ball is null.
If you want to avoid this situation, use an IF VALID node and only read the Active property down the “Is Valid” exec pin.