commitBlobTransaction: fix nil pointer (#23)

* fix nil pointer

* add comment

* address comments

miner/worker.go

@@ -389,14 +389,24 @@ func (miner *Miner) commitTransaction(env *environment, tx *types.Transaction) e
 
 func (miner *Miner) commitBlobTransaction(env *environment, tx *types.Transaction) error {
 	sc := tx.BlobTxSidecar()
-	if sc == nil && env.isEffectivelySequencing() /* we want to allow blob tx without blobs when it's deriving */ {
-		panic("blob transaction without blobs in miner")
+	var nblobs int
+	if sc == nil {
+		if env.isEffectivelySequencing() /* we want to allow blob tx without blobs when it's deriving */ {
+			panic("blob transaction without blobs in sequencing")
+		} else { // deriving, which does not have the sidecar
+			nblobs = len(tx.BlobHashes())
+		}
+	} else {
+		if !env.isEffectivelySequencing() {
+			panic("blob transaction with blobs in derivation")
+		}
+		nblobs = len(sc.Blobs)
 	}
 	// Checking against blob gas limit: It's kind of ugly to perform this check here, but there
 	// isn't really a better place right now. The blob gas limit is checked at block validation time
 	// and not during execution. This means core.ApplyTransaction will not return an error if the
 	// tx has too many blobs. So we have to explicitly check it here.
-	if (env.blobs+len(sc.Blobs))*params.BlobTxBlobGasPerBlob > params.MaxBlobGasPerBlock {
+	if (env.blobs+nblobs)*params.BlobTxBlobGasPerBlob > params.MaxBlobGasPerBlock {
 		return errors.New("max data blobs reached")
 	}
 	receipt, err := miner.applyTransaction(env, tx)