In Kibana Watcher, I'm trying to use the average results from a nested aggregation of a bucket on a condition within a Kibana Watcher but getting an null reference error when running a simulate on the Watcher

"condition": { "script": { "source": "ctx.payload.aggregations.modules.buckets.metricAgg.size() >= 1", "lang": "painless" } }

This is my nested aggregation:

"aggregations": {
            "modules": {
              "terms": {
                "field": "host.hostname.keyword",
                "size": 8,
                "min_doc_count": 1
              },
              "aggregations": {
                "metricAgg": {
                  "avg": {
                    "field": "stats"
                  }
                }
              }
            }
          }

My aggregation result is below:

"aggregations": {
          "modules": {`
            "doc_count_error_upper_bound": 0,`
            "sum_other_doc_count": 0,`
            "buckets": [`
              {
                "doc_count": 218,
                "metricAgg": {
                  "value": 1.8669724770642202
                },
                "key": "server1"
              },
              {
                "doc_count": 217,
                "metricAgg": {
                  "value": 2.096774193548387
                },
                "key": "server2"
              },
              {
                "doc_count": 215,
                "metricAgg": {
                  "value": 2.1116279069767443
                },
                "key": "server3"
              },
              {
                "doc_count": 212,
                "metricAgg": {
                  "value": 1.919811320754717
                },
                "key": "server4"
              },
              {
                "doc_count": 1,
                "metricAgg": {
                  "value": 1
                },
                "key": "server5"
              }
            ]
          }
        }
      }```

I'm receiving the following error when attempting to simulate the watcher

"exception": { "type": "script_exception", "reason": "runtime error", "script_stack": [ "ctx.payload.aggregations.modules.buckets.metricAgg.size() >= 1", " ^---- HERE" ],

"caused_by": {
  "type": "illegal_argument_exception",
  "reason": "Illegal list shortcut value [metricAgg].",
  "stack_trace": "java.lang.IllegalArgumentException: Illegal list shortcut value [metricAgg].\n\tat 

Tldr;

You can not access metricAgg directly from buckets.

Buckets holds an array of objects each containing metricAgg. If you wanted to access a specific metricAgg value, you would need to do:

ctx.payload.aggregations.modules.buckets[0].metricAgg.value // should yeild 1.8669724770642202