fix: Eth JSON-RPC API: eth_getTransactionByHash should return nil when not found

[raulk]

Related Issues

Hardhat users are having troubles deploying contracts to Wallaby via Hardhat.

The problem was introduced in 20f27af. That commit introduced the ability to resolve transactions pending in the mpool, but incorrectly returned an error when the transaction was not found. Eth clients expect a nil here, and Hardhat will send a tx and then poll the endpoint. But it will fail if an error is returned.

And one would think: if Wallaby users are deploying via Glif endpoints, then surely the Glif endpoint should be able to find the transaction within its mpool, right? Where this likely goes sideways is with load balancing.

1. The contract is deployed through origin node A (eth_sendRawTransaction).
2. The call to fetch the tx is routed to node B (eth_getTransactionByHash), which hasn't had the tx replicated to its mpool yet. If this request had gone to A, I posit we wouldn't be seeing this issue now.

Proposed Changes

Return nil from eth_getTransactionByHash when not found.

Additional Info

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