Riot, why hasn't there been a skin making contest?

I thought it would be awesome to have a contest where you could design your own skin concept and the winner gets its idea made into a skin. There has been plenty of contests similiar to this in other games and they have all been very popular. I would love to know if this could be possible. Actually I have no idea why it couldn't be done and why it hasn't been done before (right?)
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