Spring Cloud Feign Client @RequestParam with List parameter creates a wrong request

I had the same issue with multiple occurence of the parametre instead of the expected comma separated sequence of items. The solution was really simple:

In my feign client I used arrays

feignClient.get(new Long[]{1L,2L,3L})

instead of collection/list:

feignClient.get(Arrays.asList(1L,2L,3L))