Attack entity when it has a tag?

I wish my mob would attack an animal, but only if that animal has a specific tag.

In moba AI I tried to add a condition to start the attack. When I gave it to check the tag at the target entity, it checked my mob's tag. And when I gave "get entity target entity" it caused a null error, which is logical because no entity is a target yet.

Anyone know how to fix this problem?