MAGETWO-45447: SQL error after search in Billing Agreements grid in Admin

- Fixed applying filter for created_at and updated_at fields

Author: Liukshyn Roman

app/code/Magento/Paypal/Model/ResourceModel/Billing/Agreement/Collection.php

@@ -90,4 +90,17 @@ public function addCustomerDetails()
         );
         return $this;
     }
+
+    /**
+     * @param array|string $field
+     * @param null|string|array $condition
+     * @return $this
+     */
+    public function addFieldToFilter($field, $condition = null)
+    {
+        if (in_array($field , ['created_at', 'updated_at'])) {
+            $field = 'main_table.' .$field;
+        }
+        return parent::addFieldToFilter($field, $condition); // TODO: Change the autogenerated stub
+    }
 }