@Override
    @SuppressWarnings("unchecked")
    public <T, R> R getGroup(GroupExpression<T, R> definition) {
        for (GroupExpression<?, ?> def : groupExpressions) {
            if (def.equals(definition)) {
                return (R) groupCollectorMap.get(def.getExpression()).get();
            }
        }
        throw new NoSuchElementException(definition.toString());
    }
Default implementation of the Group interface

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