Fix in SqlResultProvider.getKeys().

model/SqlResultProvider.php

@@ -72,7 +72,8 @@ class SqlResultProvider
 
     public function getKeys()
     {
-        return array_keys($this->result);
+        $this->defineResultItems();
+        return array_keys($this->result_items);
     }
 
     /**
@@ -112,4 +113,4 @@ class SqlResultProvider
     {
         return $this->result->affectedRows();
     }
-}
+}