@Override
    public <T> JPAInsertClause set(Path<T> path, Expression<? extends T> expression) {
        if (expression != null) {
            inserts.put(path, expression);
        } else {
            setNull(path);
        }
        return this;
    }
UpdateClause implementation for JPA

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