@Override
    public Void visit(SubQueryExpression<?> query, Void context) {
        append("(");
        serialize(query.getMetadata(), false, null);
        append(")");
        return null;
    }
{@code JPQLSerializer} serializes Querydsl expressions into JPQL syntax.

@author tiwe
querydsl-jpa/src/main/java/com/querydsl/jpa/JPQLSerializer.java