如何使用Jolt从JSON字符串中的所有位置删除字段"last_update“？

[
  {
    "operation": "remove",
    "spec": {
      "*": {
        "last_update": ""
      }
    }
  }
]

import com.bazaarvoice.jolt.Chainr;
import com.bazaarvoice.jolt.JsonUtils;

public class JoltExample {
    public static void main(String[] args) {
        String jsonInput = "{\"key1\": {\"last_update\": \"2022-01-01\"}, \"key2\": {\"last_update\": \"2022-01-02\"}}";
        String joltSpec = "[{\"operation\": \"remove\", \"spec\": {\"*\": {\"last_update\": \"\"}}}]";

        Chainr chainr = Chainr.fromSpec(JsonUtils.jsonToList(joltSpec));
        Object transformedOutput = chainr.transform(JsonUtils.jsonToObject(jsonInput));

        System.out.println(transformedOutput);
    }
}