ElasticsearchClient._transportOptions() should not return null

[swallez]

Java API client version

7.16

Java version

all

Elasticsearch Version

all

Problem description

ElasticsearchClient._transportOptions() returns null if no options were set on the client.

It would be more convenient to have this method default to returning the underlying transport's option in that case.

Similary it would be more convient to have withTransportOptions accept a builder lambda that augments existing options.

[tongdaoqa]

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