diff --git a/src/Filter/StringFilter.php b/src/Filter/StringFilter.php
index 60389e5e..be45a81a 100644
--- a/src/Filter/StringFilter.php
+++ b/src/Filter/StringFilter.php
@@ -55,7 +55,7 @@ protected function filter(ProxyQueryInterface $query, string $field, FilterData
             return;
         }
 
-        $value = trim($data->getValue());
+        $value = trim((string) $data->getValue());
 
         if ('' === $value) {
             return;
diff --git a/tests/Filter/CallbackFilterTest.php b/tests/Filter/CallbackFilterTest.php
index fb660af5..25a26acc 100644
--- a/tests/Filter/CallbackFilterTest.php
+++ b/tests/Filter/CallbackFilterTest.php
@@ -57,7 +57,7 @@ public function testFilterMethodEmpty(): void
         $filter = new CallbackFilter();
         $filter->initialize('field_name', [
             'field_name' => self::DEFAULT_FIELD_NAME,
-            'callback' => [$this, 'customCallback'],
+            'callback' => $this->customCallback(...),
         ]);
 
         $filter->apply($builder, FilterData::fromArray([]));
@@ -72,7 +72,7 @@ public function testFilterMethodNotEmpty(): void
         $filter = new CallbackFilter();
         $filter->initialize('field_name', [
             'field_name' => self::DEFAULT_FIELD_NAME,
-            'callback' => [$this, 'customCallback'],
+            'callback' => $this->customCallback(...),
         ]);
 
         $filter->apply($builder, FilterData::fromArray(['value' => 'myValue']));