Search resources with reference is null

Question

Maybe, I misunderstood something in search mechanism in FHIR. But I have found a way if I have to find some objects which any value in some parameter.
For example, I wanted to build organization tree, in this case I have to know objects on a "first level" of this tree. And I think it should be an objects with empty partOf property. But documentation says nothing about it.
Or maybe there is another way how to achieve it?

Answer 1

Use the :missing modifier. (http://hl7.org/fhir/2016sep/search.html#modifiers)

E.g.

Organization?partof:missing=true