[BUG] NullPointerException calling BlobBatchClient.submitBatchWithResponse()

[lightningrob]

Describe the bug
When calling BlobBatchClient.submitBatchWithResponse() containing a batch of deletions, throws the NPE below. This does not always happen, maybe 10% of the time.

Exception or Stack Trace
java.lang.NullPointerException
at com.azure.storage.blob.batch.BlobBatch.getContentLength(BlobBatch.java:339)
at com.azure.storage.blob.batch.BlobBatchAsyncClient.submitBatchWithResponse(BlobBatchAsyncClient.java:120)
at com.azure.storage.blob.batch.BlobBatchClient.submitBatchWithResponse(BlobBatchClient.java:87)
at com.github.ambry.cloud.azure.BatchBlobDeletionTest.purgeBlobs(BatchBlobDeletionTest.java:126)
at com.github.ambry.cloud.azure.BatchBlobDeletionTest.testBatchDeletion(BatchBlobDeletionTest.java:113)
at com.github.ambry.cloud.azure.BatchBlobDeletionTest.main(BatchBlobDeletionTest.java:66)

To Reproduce
Run the attached main class (executes in a loop) until the exception occurs.

Code Snippet
BlobBatch blobBatch = blobBatchClient.getBlobBatch();
List responseList = new ArrayList<>();
for (String blobName : blobNames) {
responseList.add(blobBatch.deleteBlob(containerName, blobName));
}
int purgeCount = 0;
blobBatchClient.submitBatchWithResponse(blobBatch, false, Duration.ofHours(1), Context.NONE);

Expected behavior
Expect the call to succeed.

Screenshots
N/A

Setup (please complete the following information):

• OS: MacOS 10.15.2
• IDE : IntelliJ
• Version of the Library used: azure-storage-blob-12.0.0.jar

Additional context
Need to supply program with system property azure.storage.connection.string pointing to your Azure storage account.
Note: The same program sometimes fails with UnsupportedOperationException. (See issue #7255.)

Information Checklist
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BatchBlobDeletionTest.java.txt

[alzimmermsft]

@lightningrob I have tried to replicate this issue given the code sample given, haven't hit the case where this comes up. This may be resolved by the changes made based on the investigation of #7255

At a high level the cause of this would be a null value being added to the internal batch queue, but what is interesting is that all add calls are using ByteBuffer.wrap which should return a ByteBuffer or throw a NullPointerException if the byte[] being wrapped is null. My hypothesis is that, given the investigation of #7255, multiple threads are mutating the not thread-safe queue resulting in a size increment without adding an element.

[alzimmermsft]

This issue should be resolved by the most recently release version of Azure Storage Blob Batch.

[alzimmermsft]

Resolved by PR #6882