l2geth: fix `eth_getBlockRange` (#2390)

.changeset/fast-actors-allow.md

+---
+'@eth-optimism/l2geth': patch
+---
+
+Fix `eth_getBlockRange`

l2geth/internal/ethapi/api.go

@@ -51,8 +51,9 @@ import (
 )
 
 var (
-	errNoSequencerURL = errors.New("sequencer transaction forwarding not configured")
-	errStillSyncing   = errors.New("sequencer still syncing, cannot accept transactions")
+	errNoSequencerURL  = errors.New("sequencer transaction forwarding not configured")
+	errStillSyncing    = errors.New("sequencer still syncing, cannot accept transactions")
+	errBlockNotIndexed = errors.New("block in range not indexed, this should never happen")
 )
 
 const (
@@ -780,9 +781,12 @@ func (s *PublicBlockChainAPI) GetBlockRange(ctx context.Context, startNumber rpc
 	// For each block in range, get block and append to array.
 	for number := startNumber; number <= endNumber; number++ {
 		block, err := s.GetBlockByNumber(ctx, number, fullTx)
-		if block == nil || err != nil {
+		if err != nil {
 			return nil, err
 		}
+		if block == nil {
+			return nil, errBlockNotIndexed
+		}
 		blocks = append(blocks, block)
 	}
 	return blocks, nil