Merge pull request #312 from OffchainLabs/nil-header-check

Fix requested block ahead of current block check

arbitrum/apibackend.go

@@ -535,7 +535,7 @@ func (a *APIBackend) StateAndHeaderByNumberOrHash(ctx context.Context, blockNrOr
 	hash, ishash := blockNrOrHash.Hash()
 	bc := a.BlockChain()
 	// check if we are not trying to get recent state that is not yet triedb referenced or committed in Blockchain.writeBlockWithState
-	if ishash && header.Number.Cmp(bc.CurrentBlock().Number) > 0 && bc.GetCanonicalHash(header.Number.Uint64()) != hash {
+	if ishash && header != nil && header.Number.Cmp(bc.CurrentBlock().Number) > 0 && bc.GetCanonicalHash(header.Number.Uint64()) != hash {
 		return nil, nil, errors.New("requested block ahead of current block and the hash is not currently canonical")
 	}
 	return a.stateAndHeaderFromHeader(ctx, header, err)