As an editor I want to query for data based on existence of references.
**Problem:**
We currently don't allow querying for statements with references or without references.
**Example:**
- All items that are instance of human and have date of birth statement without the reference.
**Screenshots/mockups:**
TO-DO
**BDD**
GIVEN a visual query
WHEN restricting your condition to statements without references
THEN the output only contains results with statements lacking references for that statement
GIVEN a visual query
WHEN restricting your condition to statements with references
THEN the output only contains results with statements having references for that statement
**Acceptance criteria:**
[ ] Filter for statements with/without references is applied when selected
**Open questions:**