Alternative implementation of Stringer interface

[gnwgnw]

JSON marshaling allows to log a value of optional fields instead of addresses.

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• [ ] If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• [x] Did you squash your changes to a single commit? (not required, but preferred)
• [x] Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
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[fishy]

also cc @dcelasun

[Jens-G]

What's the status of this one?