Getting null parameter in apex controller from lightning controller

Its very strange, I created a new component and copied code from old component and now its working. I think problem was something else, not in the code. Thank You guys for your help. I really appreciate.

I just had the same problem. I already had 2 parameters and wanted to add 3rd, but it was always null or internal server error, no matter what i did. So in act of desperation I have cleared cookies for the site and it worked.

So if anybody else has this problem again - clear your cookies!

Clearing cookies solved this issue 100%