starlark with aggregation trigger goroutine panic

[philographer]

Relevant telegraf.conf:

• telegraf.conf

[agent]

[[inputs.file]]
  files = ["metrics_in_1.json"]
  data_format = "json"
  json_time_format = "unix"

[[processors.starlark]]
  order = 1
  source = '''
def apply(metric):
  metric.fields["delay"] = int(metric.time / 1000000000) - (metric.fields["time"] / 1000)
  metric.fields.pop("time")
  metric.fields.pop("timeout")
  return metric
'''

[[aggregators.minmax]]
  period = "60s"
  drop_original = true

[[outputs.file]]
  files = ["stdout", "metrics_delay_max.out"]

• metrics_in_1.json

{"time": 1594971809000, "timeout": 100}

System info:

• Telegraf Version: telegraf-1.15.0~rc3
• Operating System: Mac OS 10.15.5 (19F101)

Docker

• X

Steps to reproduce:

• $ telegraf --config telegraf.conf

Expected behavior:

• processor: starlark + aggregator: minmax => Aggregation Success

Actual behavior:

• Error msg

2020-07-17T07:52:40Z D! [aggregators.minmax] Updated aggregation range [2020-07-17 16:52:40 +0900 KST, 2020-07-17 16:52:50 +0900 KST]
panic: runtime error: index out of range [0] with length 0

goroutine 12 [running]:
github.com/influxdata/telegraf/plugins/processors/starlark.(*Starlark).Add(0xc0005d5c00, 0x2f58260, 0xc0008ce380, 0x2f49200, 0xc00020a060, 0x0, 0x0)
/go/src/github.com/influxdata/telegraf/plugins/processors/starlark/starlark.go:127 +0xa4a
github.com/influxdata/telegraf/models.(*RunningProcessor).Add(0xc0000a5a70, 0x2f58260, 0xc0008ce380, 0x2f49200, 0xc00020a060, 0x0, 0x0)
/go/src/github.com/influxdata/telegraf/models/running_processor.go:95 +0x106
github.com/influxdata/telegraf/agent.(*Agent).runProcessors.func1(0xc0005d0000, 0xc0001883e0)
/go/src/github.com/influxdata/telegraf/agent/agent.go:541 +0x156
created by github.com/influxdata/telegraf/agent.(*Agent).runProcessors
/go/src/github.com/influxdata/telegraf/agent/agent.go:536 +0x90

Additional info:

[danielnelson]

Thanks for the report, we will include the fix for this in 1.15.0-rc4.