A null pointer exception occurred on elasticsearch sink/source when the job configure transformer.

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Describe the bug
A null pointer exception occurred on elasticsearch sink/source when the job configure transformer.

To Reproduce
Steps to reproduce the behavior:
job .json

{
  "job": {
    "content": [
      {
        "reader": {
          "parameter": {
            "username": "",
            "password": "",
            "cat": "insert,delete,update",
            "jdbcUrl": "jdbc:mysql://localhost:3306/telemetry?useSSL=false",
            "host": "localhost",
            "port": 3306,
            "start": {
            },
            "table": [
              "flinkx_test"
            ],
            "splitUpdate": true,
            "pavingData": true,
            "column": [
              {
                "name": "id",
                "type": "BIGINT"
              },
              {
                "name": "user_id",
                "type": "BIGINT"
              },
              {
                "name": "name",
                "type": "VARCHAR"
              },
              {
                "name": "update_time",
                "type": "DATETIME"
              }
            ]
          },
          "table": {
            "tableName": "sourceTable"
          },
          "name": "binlogreader"
        },
        "writer": {
          "parameter": {
            "column": [
              {
                "name": "id",
                "type": "long"
              },
              {
                "name": "userId",
                "type": "long"
              },
              {
                "name": "name",
                "type": "text"
              },
              {
                "name": "updateTime",
                "type": "date"
              }
            ],
            "hosts": [
            ],
            "index": "flinx_target_test"
          },
          "name": "elasticsearch7writer"
        },
        "transformer": {
          "transformSql": "select id,user_id,name,update_time from sourceTable where id<=3"
        }
      }
    ],
    "setting": {
      "speed": {
        "bytes": 0,
        "channel": 1
      }
    }
  }
}

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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