Jaeger collector crashed accidentally due to samara return nil error

[Betula-L]

Describe the bug
Collector panic when print error log since e.Err is nil.

jaeger/plugin/storage/kafka/writer.go

Line 60 in b8ccf73

logger.Error(e.Err.Error())

It may be caused by sarama bug which return unexpected nil to error channel. It's hard to track the root cause of sarama sdk.

https://github.com/Shopify/sarama/blob/0616f68815691527d3b6ab4d95a2881e09400fe3/async_producer.go#L1072

Expected behavior

However, jaeger should not concern about it, just wrap e.Err.

Do not panic collector because of kafka sdk bug.

Version (please complete the following information):

• OS: Linux
• Jaeger version: v1.16.0
• Deployment: Docker

Additional context

panic logs:

env:prod
log:panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x10aca5f]
goroutine 42 [running]:
github.com/jaegertracing/jaeger/plugin/storage/kafka.NewSpanWriter.func1(0x161c860, 0xc00079e310, 0xc00010ac00, 0x15f4c80, 0xc000386ce0, 0x15f4c80, 0xc000386d50)
	github.com/jaegertracing/jaeger/plugin/storage/kafka/writer.go:54 +0x12f
created by github.com/jaegertracing/jaeger/plugin/storage/kafka.NewSpanWriter
	github.com/jaegertracing/jaeger/plugin/storage/kafka/writer.go:50 +0x273