Why do fields extracted from JSON by spath in eval result in null?

[stricq]

I cannot use any of the fields extracted by spath inside an eval.  The result is always null.

Input: (formatted for easy reading)

{
  "meta": {
    "emit_interval_s": 600
  },
  "operations": {
    "kv": {
      "Get": {
        "total_count": 4,
        "percentiles_us": {
          "75": 17747.0,
          "95": 18706.0,
          "98": 18706.0,
          "99": 18706.0,
          "100": 18706.0
        }
      },
      "GetClusterConfig": {
        "total_count": 708,
        "percentiles_us": {
          "75": 13723.0,
          "95": 14339.550000000001,
          "98": 14567.56,
          "99": 18207.0,
          "100": 18207.0
        }
      },
      "GetMeta": {
        "total_count": 4,
        "percentiles_us": {
          "75": 15776.75,
          "95": 16761.0,
          "98": 16761.0,
          "99": 16761.0,
          "100": 16761.0
        }
      }
    }
  }
}

And this is query:

| spath input=json_field | eval a=operations.kv.Get.percentiles_us.100 | table json_field operations.kv.Get.percentiles_us.100 a

In the output, a is always null but the operations.kv.Get.percentiles_us.100 always displays the correct value.

What's happening here?

[stricq · Accepted solution]

Of course, I've found the answer already.  The trick is to use rename.

| rename operations.kv.Get.total_count as totalCount, operations.kv.Get.percentiles_us.100 as getPercentile100us | eval getPercentile100ms=(getPercentile100us/1000)