Fix nil pointer dereference in TraceBlockByHash

[jcbucb]

Summary

• Adds nil check for tx.Result before accessing tx.Result.Type in TraceBlockByHash
• Prevents panic when debug_traceBlockByHash returns a trace entry with a null result

Root Cause

In TraceBlockByHash, the code checks tx.Result.Type == "" (line 451) without first checking if tx.Result is nil. The Result field is a pointer (*Call), so when the RPC returns {"result": null} for a trace entry, accessing .Type on a nil pointer causes a panic.

// ❌ Before
if tx.Result.Type == "" {  // panics if tx.Result is nil

// ✅ After
if tx.Result == nil || tx.Result.Type == "" {

Context

This panic is being observed in production on Sei EVM (rosetta-seievm) during /block requests. The stack trace:

github.com/coinbase/rosetta-geth-sdk/client.(*SDKClient).TraceBlockByHash(...)
    client/client.go:452

Test plan

• Deploy downstream consumers to dev and monitor for panics disappearing

🤖 Generated with Claude Code

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2