Imroved UserIndex:find() to only search user if query isn't empty

system/src/Grav/Common/Flex/Users/UserIndex.php

@@ -80,6 +80,7 @@ class UserIndex extends FlexIndex
      */
     public function find($query, $fields = ['username', 'email']): UserInterface
     {
+        if (is_string($query) && $query !== '') {
             foreach ((array)$fields as $field) {
                 if ($field === 'key') {
                     $user = $this->get($query);
@@ -98,6 +99,7 @@ class UserIndex extends FlexIndex
                     return $user;
                 }
             }
+        }
 
         return $this->load('');
     }