better peewee syntax

arkindex_worker/worker/element.py

@@ -410,14 +410,21 @@ class ElementMixin(object):
                 query = query.where(CachedElement.type == type)
             if worker_version is not None:
                 # If worker_version=False, filter by manual worker_version e.g. None
-                worker_version_id = worker_version if worker_version else None
-                query = query.where(
-                    CachedElement.worker_version_id == worker_version_id
-                )
+                worker_version_id = worker_version or None
+                if worker_version_id:
+                    query = query.where(
+                        CachedElement.worker_version_id == worker_version_id
+                    )
+                else:
+                    query = query.where(CachedElement.worker_version_id.is_null())
+
             if worker_run is not None:
                 # If worker_run=False, filter by manual worker_run e.g. None
                 worker_run_id = worker_run or None
-                query = query.where(CachedElement.worker_run_id == worker_run_id)
+                if worker_run_id:
+                    query = query.where(CachedElement.worker_run_id == worker_run_id)
+                else:
+                    query = query.where(CachedElement.worker_run_id.is_null())
 
             return query
         else: