Java codegen, when post a String parameter, unexpected quote in json

My code :

@Path("/{id}")
  @PUT
  @Consumes({"application/json"})
  @ApiOperation(value = "Update Tab info", notes = "test")
  public Result put(@PathParam("id")final String id, String tab) {
    return super.put(id, tab);
  }

swagger-spec

"put": {
                "tags": [
                    "tab"
                ],
                "summary": "Update Tab info",
                "description": "If current user is owner, he can update all attribute. If current user is signer, he could only update data",
                "operationId": "put",
                "consumes": [
                    "application/json"
                ],
                "produces": [
                    "application/json"
                ],
                "parameters": [
                    {
                        "name": "id",
                        "in": "path",
                        "required": true,
                        "type": "string"
                    },
                    {
                        "in": "body",
                        "name": "body",
                        "required": false,
                        "schema": {
                            "type": "string"
                        }
                    }
                ],
                "responses": {
                    "200": {
                        "description": "successful operation",
                        "schema": {
                            "$ref": "#/definitions/Result"
                        }
                    }

codegen generate code:

  public Result put(String id, String body) throws ApiException {
    Call call = putCall(id,body, null, null);
    Type returnType = new TypeToken<Result>(){}.getType();
    return apiClient.execute(call, returnType);
  }

When I use this method, I capture the package with wireshark
screenshot:

If I use the swagger-ui to call this API, I capture the package with wireshark
screenshot:

Start by reproducing the request from the generated Java client's put method and compare its body with the Swagger UI request; inspect the request-building path used by putCall. Done means posting a String body produces the same JSON payload without the unexpected quote.