@Override
    public void addJoin(JoinType joinType, Expression<?> expr) {
        joins = null;
        super.addJoin(joinType, expr);
    }
{@code OrderedQueryMetadata} performs no metadata validation and ensures that FROM elements are before
JOIN elements

@author tiwe
querydsl-core/src/main/java/com/querydsl/core/support/OrderedQueryMetadata.java