diff --git a/stix2/datastore/memory.py b/stix2/datastore/memory.py
index c43da8b..c1d202d 100644
--- a/stix2/datastore/memory.py
+++ b/stix2/datastore/memory.py
@@ -268,10 +268,7 @@ class MemorySource(DataSource):
                 is returned in the same form as it as added.
 
         """
-        if query is None:
-            query = FilterSet()
-        else:
-            query = FilterSet(query)
+        query = FilterSet(query)
 
         # combine all query filters
         if self.filters: