@SuppressWarnings("unchecked")
    private <T, R> R get(Expression<T> expr) {
        GroupCollector<T,R> col = (GroupCollector<T,R>) groupCollectorMap.get(expr);
        if (col != null) {
            return col.get();
        }
        throw new NoSuchElementException(expr.toString());
    }
Default implementation of the Group interface

@author sasa
@author tiwe
querydsl-core/src/main/java/com/querydsl/core/group/GroupImpl.java