public static <T> T nullif(T first, T second) {
        if (first.equals(second)) {
            return null;
        } else {
            return first;
        }
    }
{@code CollQueryFunctions} defines function implementation for use in ColQueryTemplates

@author tiwe
querydsl-collections/src/main/java/com/querydsl/collections/CollQueryFunctions.java