SDK drift: `fetchArbitrage`/`fetch_arbitrage` — explicit-null `marketA`/`marketB` produce different types (object vs `None`)

[realfishsam]

Drift

When a server payload has an explicit null for marketA/marketB, TypeScript's r.marketA || {} fallback still produces a fully-shaped (if empty) UnifiedMarket object via convertMarket({}). Python's _parse_market returns its input unchanged when it's neither a UnifiedMarket nor a dict, so r.get("marketA", {}) — which only substitutes the default when the key is absent, not when it's null — lets an explicit null flow straight through as None.

TypeScript SDK

sdks/typescript/pmxt/router.ts:615-616:

marketA: convertMarket(r.marketA || {}),
marketB: convertMarket(r.marketB || {}),

Python SDK

sdks/python/pmxt/router.py:642-643:

market_a=_parse_market(r.get("marketA", {})),
market_b=_parse_market(r.get("marketB", {})),

_parse_market (sdks/python/pmxt/router.py:28-34) returns its input unchanged when it's neither a UnifiedMarket nor a dict.

Expected

Both SDKs should produce the same type for market_a/market_b given the same wire payload — either both fall back to an empty market object, or both preserve None.

Impact

ArbitrageOpportunity.market_a/market_b is None in Python vs. a market-shaped object in TypeScript for the same payload. Any code doing opportunity.market_a.title crashes with AttributeError in Python but not in TypeScript. This is distinct from existing issue #1535, which is scoped to numeric/venue field defaulting on this same method, not the market-object type itself.

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Found by automated SDK cross-language drift audit