CURATOR-538: address from InetSocketAddress could be null as it means unresolved address

[snuyanzin]

To be aligned with contract of java.net.InetSocketAddress it should take into account that java.net.InetSocketAddress#getAddress could return null which will mean unresolved address

[tisonkun]

Thanks for your contribution @snuyanzin!

The change looks good. But I don't know how can this patch be relevant to CURATOR-538?

[snuyanzin]

hi @tisonkun thanks for the response

in fact there are 3 jira issues for the same situation CURATOR-597, CURATOR-538, CURATOR-649
every fails with NPE since the address was marked as unresolved and as a result it tries to host from address...
but at the same time for unresolved addresses address is null.... The idea is return unknown in case of unresolved addresses as for other exceptions

[tisonkun]

Thanks for your explanation!

Merging...