MetadataRequest V5 has wrong encoding for "all topics"

[dnwe]

Versions

Please specify real version numbers or git SHAs, not just "Latest" since that changes fairly regularly.
Sarama Version: 2b82435
Kafka Version: 1.1.0
Go Version: 1.11.8

Configuration

What configuration values are you using for Sarama and Kafka?

	cfg := sarama.NewConfig()
	cfg.Net.TLS.Enable = true
	cfg.Version = sarama.V1_1_0_0

Logs

[Sarama] 2019/04/10 22:08:13 Initializing new client
[Sarama] 2019/04/10 22:08:13 client/metadata fetching metadata for all topics from broker kafka-2:9092
[Sarama] 2019/04/10 22:08:19 Connected to broker at kafka-2:9092 (unregistered)
[Sarama] 2019/04/10 22:08:19 client/brokers registered new broker #2 at kafka-2:9092
[Sarama] 2019/04/10 22:08:19 client/brokers registered new broker #1 at kafka-1:9092
len(topics) received 0 topics in all metadata request

Problem Description

TL;DR if the client config version is at least 1.0.0.0 then the "full" metadata refresh always returns an empty topic list

Underlying cause

Since e3ecf7b the tryRefreshMetadata for a "full" metadata request now appears to use the V5 MetadataRequest if config version is at least 1.0.0.0

https://github.com/Shopify/sarama/blob/2b824357033b9904e3a32bf7fae2efe76f1591fd/client.go#L761-L765

However, this commit appeared to also add an additional if statement to the encoding of the request to send an empty array rather than a null if the provided topics list was an empty slice

https://github.com/Shopify/sarama/blob/2b824357033b9904e3a32bf7fae2efe76f1591fd/metadata_request.go#L13

I'm not sure why this was done as consulting the protocol guide the V5 request uses the same nullable array for topics as the V1-V4 requests.

Metadata Request (Version: 5) => [topics] allow_auto_topic_creation
topics => STRING
allow_auto_topic_creation => BOOLEAN

Field	Description
topics	An array of topics to fetch metadata for. If the topics array is null fetch metadata for all topics.
allow_auto_topic_creation	If this and the broker config auto.create.topics.enable are true, topics that don't exist will be created by the broker. Otherwise, no topics will be created by the broker.

[dnwe]

Unfortunately this bug is included in the just-released v1.22.0 milestone