Accessed none error for function input

I get an accessed none error for the “Other Actor” variable for the following call of a function:

And here is the function itself:

I hope I’m not misinterpreting your blueprint but it looks like the issue is caused by the second apply point damage in the second picture. In image one you call the function and don’t pass in a instigator actor, then when it enters the methods you still choose to pass the NULL actor into your program after you checked if it is valid. What you need to do is make sure the Other Actor is being set correctly and add some handling in your function for when the actor isn’t valid.

I think that could have been one of the problems, so thank you. However I found the actual source of the problem. I think your suggestion would have “only” been another workaround for the actual issue. I will post it as an answer in a second.
As a result of the solution I was able to get rid of most of the “Is Valid” checks I put in to get rid of the error.

I used the “Other Actor” to calculate the normal impulse that I passed into the function. So I forgot an Is Valid Check a step earlier.
So the morale is always check all your input pins.

As a result I was able to get rid of both Is Valid Checks shown in the images. The one before the function and the one inside the function.