batch-submitter: handle error case explicitly

It was possible to return from a function directly
into destructuring an array when the return value
was polymorphic in either being an array or undefined.
The undefined case is handled explicitly now and an
error is thrown with a useful error message instead of
something that would require looking at the source code
and knowing nodejs error types to find out what the
problem was.

.changeset/great-buckets-bow.md

@@ -0,0 +1,5 @@
+---
+'@eth-optimism/batch-submitter': patch
+---
+
+Handle error case more explicity when creating invalid batch

packages/batch-submitter/src/batch-submitter/tx-batch-submitter.ts

@@ -195,8 +195,12 @@ export class TransactionBatchSubmitter extends BatchSubmitter {
       return
     }
 
-    const [batchParams, wasBatchTruncated] =
-      await this._generateSequencerBatchParams(startBlock, endBlock)
+    const params = await this._generateSequencerBatchParams(startBlock, endBlock)
+    if (!params) {
+      throw new Error(`Cannot create sequencer batch with params start ${startBlock} and end ${endBlock}`)
+    }
+
+    const [batchParams, wasBatchTruncated] = params
     const batchSizeInBytes = encodeAppendSequencerBatch(batchParams).length / 2
     this.logger.debug('Sequencer batch generated', {
       batchSizeInBytes,