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Parses a SEP-31 sep12 JSON object into a Sep31Sep12TypesInfo.
The function tolerates missing sender, receiver, or types sub-objects by treating them as empty maps — the anchor may legitimately omit either side if no KYC is required for that role. Entries whose description is missing or not a string are silently skipped.
Return
The parsed Sep31Sep12TypesInfo.
Parameters
json
The sep12 JSON object from the SEP-31 GET /info response.
Throws
if the underlying JSON shape is malformed.