diff --git a/system/Validation/FileRules.php b/system/Validation/FileRules.php
index ea1a6f678379..2becb34b1950 100644
--- a/system/Validation/FileRules.php
+++ b/system/Validation/FileRules.php
@@ -133,7 +133,7 @@ public function is_image(?string $blank, string $params): bool
 
             // We know that our mimes list always has the first mime
             // start with `image` even when then are multiple accepted types.
-            $type = Mimes::guessTypeFromExtension($file->getExtension());
+            $type = Mimes::guessTypeFromExtension($file->getExtension()) ?? '';
 
             if (mb_strpos($type, 'image') !== 0) {
                 return false;
diff --git a/tests/_support/Validation/uploads/abc77tz b/tests/_support/Validation/uploads/abc77tz
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/system/Validation/FileRulesTest.php b/tests/system/Validation/FileRulesTest.php
index 0a2f5356efd8..8c5ce6e142ac 100644
--- a/tests/system/Validation/FileRulesTest.php
+++ b/tests/system/Validation/FileRulesTest.php
@@ -41,7 +41,9 @@ final class FileRulesTest extends CIUnitTestCase
 
     protected function setUp(): void
     {
+        $this->resetServices();
         parent::setUp();
+
         $this->validation = new Validation((object) $this->config, Services::renderer());
         $this->validation->reset();
 
@@ -229,6 +231,7 @@ public function testIsntImage(): void
             'type'     => 'application/address',
             'error'    => UPLOAD_ERR_OK,
         ];
+
         $this->validation->setRules(['avatar' => 'is_image[stuff]']);
         $this->assertFalse($this->validation->run([]));
     }