Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $

背景
需要将自研系统中的审批流数据同步到飞书审批中心。

资料
使用的SDK：com.larksuite.oapi:oapi-sdk:2.0.20

报错
com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:226)
at com.google.gson.Gson.fromJson(Gson.java:922)
at com.google.gson.Gson.fromJson(Gson.java:887)
at com.google.gson.Gson.fromJson(Gson.java:836)
at com.google.gson.Gson.fromJson(Gson.java:808)
at com.lark.oapi.core.utils.UnmarshalRespUtil.unmarshalResp(UnmarshalRespUtil.java:22)
at com.lark.oapi.service.approval.v4.ApprovalService$ExternalInstance.create(ApprovalService.java:587)

期望
先看代码
// 反序列化
CreateExternalInstanceResp resp = UnmarshalRespUtil.unmarshalResp(httpResponse, CreateExternalInstanceResp.class);
if (resp == null) {
log.error(String.format(
"%s,callError,req=%s,respHeader=%s,respStatusCode=%s,respBody=%s,", "/open-apis/approval/v4/external_instances"
, Jsons.DEFAULT.toJson(req), Jsons.DEFAULT.toJson(httpResponse.getHeaders()),
httpResponse.getStatusCode(), new String(httpResponse.getBody(),
StandardCharsets.UTF_8)));
throw new IllegalArgumentException("The result returned by the server is illegal");
}
UnmarshalRespUtil.unmarshalResp方法在执行时并没有做异常处理，导致CreateExternalInstanceResp resp = UnmarshalRespUtil.unmarshalResp(httpResponse, CreateExternalInstanceResp.class);执行时，直接抛出异常，不会继续向下执行，并打印出返回结果日志。

希望完善这个BUG，抛出异常可以，但应该要输出返回结果是什么，而不是JSON序列化的错误。

Start with UnmarshalRespUtil.unmarshalResp, called from ApprovalService$ExternalInstance.create for /open-apis/approval/v4/external_instances. Trace how the HTTP response body is handled when Gson raises JsonSyntaxException, then verify that failures preserve or log the returned response content instead of exposing only the deserialization error.