Accessed none trying to read property

So I’m on my 8th and final course for Coursera, and as I’m working around in the second module, I came across this error involving my stealth mechanic.

It tells me that I should set a scalar parameter but they’re already set, at least, I think they’re already set.

I don’t see the error here? The error points to the f Stealth Off function as seen below. I wish the course covered this error already.

I’m already in the process of area of effect based attacks and this just came out. I’m not going to bother asking their AI for help, so I’m wondering if anyone here can help me out.

Thanks.

Just to add to this, the error is blueprint runtime error: accessed none trying to read property mesh_material_0 . node: set scalar parameter value graph: fstealth_off function: f stealth off blueprint: bp_character_coursera_player