This fragment https://github.com/spring-projects/spring-data-commons/blob/ee004b0f10c50fdeeace96f62467e152da4590d2/src/main/java/org/springframework/data/repository/query/ResultProcessor.java#L146-L148 assumes that if the method is a slice method, the non converted result is already a slice, which does fail if it is a plain collection.