diff --git a/components/engine/api/swagger.yaml b/components/engine/api/swagger.yaml
index 6aeb711e59..f8adfe9feb 100644
--- a/components/engine/api/swagger.yaml
+++ b/components/engine/api/swagger.yaml
@@ -1082,6 +1082,7 @@ definitions:
     type: "object"
     additionalProperties:
       type: "array"
+      x-nullable: true
       items:
         $ref: "#/definitions/PortBinding"
     example:
@@ -1106,7 +1107,6 @@ definitions:
       PortBinding represents a binding between a host IP address and a host
       port.
     type: "object"
-    x-nullable: true
     properties:
       HostIp:
         description: "Host IP address that the container's port is mapped to."