fix(eth): serialize empty lists as [] instead of null

[sudo-shashank]

Summary of changes

Changes introduced in this pull request:

• Use NotNullVec instead of Vec for empty lists so they are never null.

Reference issue to close (if applicable)

Closes #7205

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

Summary

• Bug Fixes

  • Updated Ethereum JSON-RPC responses for eth_accounts, eth_getBlockReceipts*, and trace_* to always return non-null arrays ([] for empty results) instead of null.
  • Adjusted transaction accessList behavior: typed transactions now serialize empty accessList as [], while legacy transactions omit accessList.

• Documentation

  • Updated OpenRPC specification to reflect non-null array results and the new accessList requirements.

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Walkthrough

NotNullVec<T> gains Default and GetSize derives to enable proper empty-array and size-tracking semantics. Seven Ethereum RPC methods (EthAccounts, EthGetBlockReceipts, EthGetBlockReceiptsLimited, EthTraceBlock, EthTraceTransaction, EthTraceReplayBlockTransactions, EthTraceFilter) are converted from returning Vec<T> to NotNullVec<T>. ApiEthTx.access_list field is changed from Vec<EthHash> to Option<NotNullVec<EthHash>>, ensuring empty lists serialize as [] rather than null. OpenRPC schemas are updated across all versions to reflect these non-nullable array contracts. Unit tests validate serialization and deserialization behavior, and a changelog entry documents the fix.

Changes

ETH empty-list serialization fix

Layer / File(s)	Summary
NotNullVec struct: Default and GetSize derives src/lotus_json/vec.rs	Adds GetSize import and extends NotNullVec<T> derive list with Default and GetSize traits.
ApiEthTx.access_list field and transaction conversions src/rpc/methods/eth.rs, src/rpc/methods/eth/eth_tx.rs	Updates ApiEthTx.access_list to Option<NotNullVec<EthHash>> with serde/schemars configuration to omit when None. Native-message and EIP-1559 transaction conversions now set access_list to Some(NotNullVec(vec![])) for empty lists. Comprehensive unit tests verify serialization (empty, populated, explicit None omission, legacy behavior) and deserialization (missing/null handling).
ETH RPC method return types switched to NotNullVec src/rpc/methods/eth.rs	Imports NotNullVec and updates seven method return types (EthAccounts, EthGetBlockReceipts, EthGetBlockReceiptsLimited, EthTraceBlock, EthTraceTransaction, EthTraceReplayBlockTransactions, EthTraceFilter) from Vec<T> to NotNullVec<T>. Handlers wrap results with NotNullVec or .map(NotNullVec). Fixes trace_filter to iterate over inner vector via block_traces.0.
OpenRPC specification schemas across all versions docs/openrpc-specs/v0.json, docs/openrpc-specs/v1.json, docs/openrpc-specs/v2.json	Updates method result schemas for Filecoin-prefixed and lowercase variants from optional/nullable arrays (required: false, type: [array, null]) to required non-nullable arrays (required: true, type: array). Updates ApiEthTx.accessList property from nullable to non-nullable array type across all spec versions.
Changelog and test snapshots CHANGELOG.md, src/tool/subcommands/api_cmd/test_snapshots.txt	Adds changelog entry for PR #7214 documenting accessList serialization alignment with go-ethereum/reth. Updates regenerated test snapshot references.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• ChainSafe/forest#6731: Changes to Ethereum trace RPC handlers (trace_block, trace-related responses) to return non-null arrays overlap with this PR's trace handler refactoring in src/rpc/methods/eth.rs.

Suggested reviewers

• hanabi1224
• LesnyRumcajs

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing empty list serialization to use [] instead of null in Ethereum RPC responses.
Linked Issues check	✅ Passed	The PR addresses all three completion criteria from #7205: verifies correct behavior against reth/go-ethereum standards, implements the fix for the accessList field serialization, and adds comprehensive regression tests.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the accessList serialization issue and aligning with Ethereum standards; no unrelated or out-of-scope modifications detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch shashank/fix-accessList

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch shashank/fix-accessList

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[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 64.08%. Comparing base (08d39a2) to head (7ca0e2d).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/rpc/methods/eth.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/lotus_json/vec.rs	84.61% <ø> (+23.07%)	⬆️
src/rpc/methods/eth/eth_tx.rs	100.00% <100.00%> (+31.81%)	⬆️
src/rpc/methods/eth.rs	65.18% <92.30%> (+0.07%)	⬆️

... and 10 files with indirect coverage changes

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[LesnyRumcajs]

API compare tests failed in | Filecoin.EthGetTransactionByBlockNumberAndIndex (20) | 18/20 | 18/20 | ⚠️ Mixed Results (CustomCheckFailed) |. This must be addressed.

[sudo-shashank]

API compare tests failed in | Filecoin.EthGetTransactionByBlockNumberAndIndex (20) | 18/20 | 18/20 | ⚠️ Mixed Results (CustomCheckFailed) |. This must be addressed.

filtering these methods until lotus fix them