GET method error on the console

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Hi guys, I'm a first-timer here. 
I'm not sure how to fix this error that I get on the console. I'm basically trying to make my own modal. I get the error after I click the close button on the modal overlay page.

Here's the error that I get on the console.

null:1 GET 404
Image (async)
createModal @ gallery-media:872
(anonymous) @ gallery-media:881

I have no idea what causes this at all. So, if anyone could point me out in the right direction. I'd really appreciate it. Thanks, guys.

here's my page