Doctrine ResultSetMapping ignores entity - php

Question

In doctrine, I want to fetch multiple entities from a native query. But I can't workout how to do it.
I have 3 entities: WBSOProject, Employee and WBSOBooking. Employees can log their work hours through a WBSOBooking entity which couples the Employee with a WBSOProject and it has an extra field for the logged hours.
To generate an overview of the worked hours per employee per project I've written the following code:
$query = "
select
project.id as project_id,
project.name,
employee.id as employee_id,
employee.bsn,
employee.name,
sec_to_time(sum(time_to_sec(wbsoBooking.total))) as balance
from wbso_projects project
inner join wbso_bookings as wbsoBooking on wbsoBooking.project_id = project.id
inner join employees as employee on employee.id = wbsoBooking.employee_id
group by project.year, project.name, employee.id, employee.name
";
$rsm = new ResultSetMapping();
$rsm
->addEntityResult("Kloktijden\\Model\\Entities\\WBSOProject", "project")
->addFieldResult("project", "project_id", "id")
->addFieldResult("project", "name", "name")
->addEntityResult("Kloktijden\\Model\\Entities\\Employee", "employee")
->addFieldResult("employee", "employee_id", "id")
->addFieldResult("employee", "bsn", "bsn")
->addFieldResult("employee", "name", "name")
->addScalarResult("balance", "balance");
$result = Model::getEntityManager()
->createNativeQuery($query, $rsm)
->getResult();
My desired result would be an array like this:
array(
[0] => array(
[0] => Kloktijden\\Model\\Entities\\WBSOProject,
[1] => Kloktijden\\Model\\Entities\\Employee,
"balance" => "00:00"
)
)
But somehow the Employee entity gets ignored, so my result looks like this:
array(
[0] => array(
[0] => Kloktijden\\Model\\Entities\\WBSOProject,
"balance" => "00:00"
)
)
So, my question is: why doesn't my resultset contain the Employee entity? And how can I fix this?