the check valve from the filler neck gas tank is missing? can't fill up with gas

[bluebombersfan]

Okay, so today I go and fill up my gas tank and I notice the check valve in the filler neck is missing. I try to fill up on gas and it seems clogged. What the heck happened?
Was someone screwing around with my truck? Did they stuff something in there? Do these check valves just dissapear on there own?

 

[adsm08]

If it fell off somehow it may be down there blocking something.