Fields missing from webservice datasource in SSRS

Question

We are using a XML webservice as a datasource for SSRS. The webservice is returning  the hierarchy of departments of our company.
The data is consumed by SSRS but some fields are missing.
This is (simplified) what is returned by the webservice:
<department>
  <nr>1</nr>
  <name>name1/name>
</department>
<department>
  <nr>2</nr>
  <name>name2/name>
  <parentdepartment>1</parentdepartment>
</department>
etc
The field parentdepartment is missing from the fieldlist, even if I add it by hand it will be empty.
At this forum I found that fields are even skipped when the first item has an empty value for a certain field so the absence of a field in the first item must certainly be the
problem. Nr 1 has no parentdepartment field.
Is there a way around this like skipping the first department, we don't need it, or forcing the SSRS-datasource to add the parentdepartment field.
As it is used by many applications we prefer not to change the webservice to skip the first or add dummy values to the first item.

Answer 1

Typically if the field doesn't show up the CR can't figure out what type it is which means when we query the DB for the field type the client/server returns the wrong type or some type that CR doesn't support.
How is the field defined on the server?
Thank you
Don