eth: fix tracer panic when running without configs + reexec (#15799)

eth/api_tracer.go

@@ -204,7 +204,7 @@ func (api *PrivateDebugAPI) traceChain(ctx context.Context, start, end *types.Bl
 	if err != nil {
 		// If the starting state is missing, allow some number of blocks to be reexecuted
 		reexec := defaultTraceReexec
-		if config.Reexec != nil {
+		if config != nil && config.Reexec != nil {
 			reexec = *config.Reexec
 		}
 		// Find the most recent block that has the state available
@@ -465,7 +465,7 @@ func (api *PrivateDebugAPI) traceBlock(ctx context.Context, block *types.Block,
 		return nil, fmt.Errorf("parent %x not found", block.ParentHash())
 	}
 	reexec := defaultTraceReexec
-	if config.Reexec != nil {
+	if config != nil && config.Reexec != nil {
 		reexec = *config.Reexec
 	}
 	statedb, err := api.computeStateDB(parent, reexec)
@@ -619,7 +619,7 @@ func (api *PrivateDebugAPI) TraceTransaction(ctx context.Context, hash common.Ha
 		return nil, fmt.Errorf("transaction %x not found", hash)
 	}
 	reexec := defaultTraceReexec
-	if config.Reexec != nil {
+	if config != nil && config.Reexec != nil {
 		reexec = *config.Reexec
 	}
 	msg, vmctx, statedb, err := api.computeTxEnv(blockHash, int(index), reexec)