diff --git a/src/Datagrid/ProxyQueryInterface.php b/src/Datagrid/ProxyQueryInterface.php
index eca46f5107..d4f01e2988 100644
--- a/src/Datagrid/ProxyQueryInterface.php
+++ b/src/Datagrid/ProxyQueryInterface.php
@@ -40,11 +40,11 @@ public function execute(array $params = [], ?int $hydrationMode = null);
      */
     public function setSortBy(array $parentAssociationMappings, array $fieldMapping): self;
 
-    public function getSortBy(): string;
+    public function getSortBy(): ?string;
 
     public function setSortOrder(string $sortOrder): self;
 
-    public function getSortOrder(): string;
+    public function getSortOrder(): ?string;
 
     /**
      * @return mixed
@@ -62,6 +62,8 @@ public function getMaxResults(): ?int;
     public function getUniqueParameterId(): int;
 
     /**
+     * Join entities from the given association mappings and return the last alias created.
+     *
      * @param mixed[] $associationMappings
      */
     public function entityJoin(array $associationMappings): string;
diff --git a/tests/App/Datagrid/ProxyQuery.php b/tests/App/Datagrid/ProxyQuery.php
index 09b08df667..94cb0abf22 100644
--- a/tests/App/Datagrid/ProxyQuery.php
+++ b/tests/App/Datagrid/ProxyQuery.php
@@ -31,7 +31,7 @@ public function setSortBy(array $parentAssociationMappings, array $fieldMapping)
         throw new \BadMethodCallException('Not implemented.');
     }
 
-    public function getSortBy(): string
+    public function getSortBy(): ?string
     {
         return 'e.id';
     }
@@ -41,7 +41,7 @@ public function setSortOrder(string $sortOrder): ProxyQueryInterface
         throw new \BadMethodCallException('Not implemented.');
     }
 
-    public function getSortOrder(): string
+    public function getSortOrder(): ?string
     {
         return 'ASC';
     }