How to write pandas dataframe to blob using azure functions blob trigger

I am trying to write pandas dataframe to outputblob stream as follows:

def main(myblob: func.InputStream,outputblob: func.Out[func.InputStream]):
    logging.info(f"Python blob trigger function processed blob \n"
                 f"Name: {myblob.name}\n"
                 f"Blob Size: {myblob.length} bytes")

    blobBinaryDataStream = io.BytesIO(myblob.read())
    reader = fastavro.reader(blobBinaryDataStream)
    # Load records in memory
    records = [r for r in reader]
    # Populate pandas.DataFrame with records
    df = pd.DataFrame.from_records(records)

    stream = io.StringIO()
    df.to_csv(stream, sep=",")
    outputblob.set(stream)

However, its writing an empty file to blob. Can anyone help with this?