Haskell - Non-exhaustive pattern for a reason I don't understand

So I'm trying to write a function that, given two lists of integers, adds the ith even number of each list and returns them in another list. In case one of the list doesn't have an ith even number, a 0 is considered. For example, if the lists are [1,2,1,4,6] and [2,2], it returns [4,6,6] ([2+2,4+2,6+0]). I have the following code:

addEven :: [Int] -> [Int] -> [Int] 
addEeven [] [] = []
addEeven (x:xs) [] = filter (\g -> g `mod`2 == 0) (x:xs)
addEven [] (y:ys) = filter (\g -> g `mod` 2 == 0) (y:ys)
addEven (x:xs) (y:ys) = (a + b):(addEven as bs)
                        where 
                          (a:as) = filter (\g -> g `mod` 2 == 0) (x:xs)
                          (b:bs) = filter (\g -> g `mod` 2 == 0) (y:ys)

When I run that with the previous example, I get:

[4,6*** Exception: ex.hs:(4,1)-(8,101): Non-exhaustive patterns in function addEven

I really can't see what I'm missing, since it doesn't work with any input I throw at it.