Error: Accessed None trying to read property reason?

I found a weird situation here:

I have this as start. Here (at the first call) I atempt to destroy a actor that not exits (not set yet).
There are no warnings or errors when I do it.

However, if I copy it before calling:

Then I will get a error msg after I exit the play mode.

Blueprint Runtime Error: “Accessed
None trying to read property
Blueprint: MainGameMode Function:
Set Hair Graph: Set Hair Node:

Interestingly, the function actually works as it should, however I don’t see why the first one doesn’t throw error after exiting from play mode, while the second one does.
They should behave the same, as the values (should be) the same in both case.

Testing with isvalid node, both reports false, however it only causes error in the last case.