NullPointerException when killing a creaking riding a dolphin

Destroying the creaking heart while the creaking is riding a dolphin results in a NullPointerException.

How to reproduce:

1. Place a creaking heart between two pale oak logs to ensure it is active.
2. Execute

   /ride @n[type=minecraft:creaking] mount @n[type=minecraft:dolphin]

3. Destroy the creaking heart of the creaking riding the dolphin.

Expected result:

A NullPointerException would not occur.

Observed result:

A NullPointerException occurs.