Panic in kafka_consumer

[sethm]

Bug report

System info:

Telegraf 1.0.0 running under Docker, using the docker image obtained from Docker Hub.

Steps to reproduce:

1. Run Telegraf under Docker, configured to consume from a Kafka topic.
2. Run InfluxDB to be populated from Telegraf
3. Fill the Kafka topic with valid JSON data

Expected behavior:

The JSON data should be consumed without error

Actual behavior:

After approximately 350000 metrics have been consumed, Telegraf panics with the following message:

2016/09/14 01:00:52 Output [influxdb] wrote batch of 1000 metrics in 125.002825ms
2016/09/14 01:00:52 Output [influxdb] wrote batch of 1000 metrics in 96.751418ms
2016/09/14 01:00:58 ERROR: Post http://influxdb:8086/write?consistency=any&db=telemetry&precision=ns&rp=: net/http: request canceled (Client.Timeout exceeded while awaiting headers)
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x5a48d6]

goroutine 30 [running]:
panic(0x12cefe0, 0xc82000a090)
    /usr/local/go/src/runtime/panic.go:481 +0x3e6
github.com/influxdata/telegraf/plugins/inputs/kafka_consumer.(*Kafka).receiver(0xc8200b40c0)
    /home/ubuntu/telegraf-build/src/github.com/influxdata/telegraf/plugins/inputs/kafka_consumer/kafka_consumer.go:131 +0x276
created by github.com/influxdata/telegraf/plugins/inputs/kafka_consumer.(*Kafka).Start
    /home/ubuntu/telegraf-build/src/github.com/influxdata/telegraf/plugins/inputs/kafka_consumer/kafka_consumer.go:117 +0x232

Additional info:

Kafka Consumer configuration:

[[inputs.kafka_consumer]]
  ## topic(s) to consume
  topics = ["nom-telemetry"]
  ## an array of Zookeeper connection strings
  zookeeper_peers = ["nom-kafka:2181"]
  ## Zookeeper Chroot
  zookeeper_chroot = "/kafka"
  ## the name of the consumer group
  consumer_group = "telegraf_metrics_consumers"
  ## Offset (must be either "oldest" or "newest")
  offset = "oldest"

  ## Data format to consume.
  ## Each data format has it's own unique set of configuration options, read
  ## more about them here:
  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
  data_format = "json"

[sparrc]

thanks for the report, this is caused by a nil error getting sent down the kafka errs channel. I didn't realize this was possible, so I'll add a nil check on the incoming error.