diff --git a/src/FacetManager/DefaultFacetManager.php b/src/FacetManager/DefaultFacetManager.php
index c033c4c..c3345a6 100644
--- a/src/FacetManager/DefaultFacetManager.php
+++ b/src/FacetManager/DefaultFacetManager.php
@@ -164,8 +164,9 @@ class DefaultFacetManager {
         $unfiltered_results = $query_type_plugin->execute();
 
         // Save unfiltered results in facet.
-        $facet->setUnfilteredResults($unfiltered_results);
-
+        if (!is_null($unfiltered_results)) {
+          $facet->setUnfilteredResults($unfiltered_results);
+        }
       }
     }
   }
diff --git a/tests/src/Unit/Plugin/query_type/SearchApiStringTest.php b/tests/src/Unit/Plugin/query_type/SearchApiStringTest.php
index cecd79f..9f15b78 100644
--- a/tests/src/Unit/Plugin/query_type/SearchApiStringTest.php
+++ b/tests/src/Unit/Plugin/query_type/SearchApiStringTest.php
@@ -24,7 +24,10 @@ class SearchApiStringTest extends UnitTestCase {
    */
   public function testQueryType() {
     $query = new SearchApiQuery([], 'search_api_query', []);
-    $facet = new Facet([], 'facets_facet');
+    $facet = new Facet(
+      ['options' => ['query_operator' => 'AND']],
+      'facets_facet'
+    );
 
     $original_results = [
       ['count' => 3, 'filter' => 'badger'],