Mathematica DiracDelta function example from Wolfram documentation

[Swamp Thing]

TL;DR

Example of DiracDelta from the Wolfram Language help doesn't seem to work, at least on Wolfram Cloud.

The page on the Wolfram function DiracDelta has this example:

Integrate[DiracDelta[x] Cos[x], {x, -Infinity, Infinity}]

It's the first example under Examples > Basic Examples. When I run it in Wolfram Cloud, it says "Invalid integration variable or limit(s) ..."
and shows this result:

What's going wrong?

Edit: here's a screenshot:

 

[Orodruin]

Have you set x to 3 earlier in your script?

 

[Swamp Thing]

O... M... G...

Yes, I have, actually

 

[Orodruin]

Try clearing x or use another integration variable.

 

[Swamp Thing]

Thanks, it works now.