The spec says that bson-formatted data has format
{source: <old-ns>, target: <new-ns>}
But the data actually uses different keys:
{original: <old-ns>, new: <new-ns>}
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Also, the renameCollection operation can fail if dropTarget is not true and the target collection already exists. No audit logging occurs in this case. It's not clear if any is necessary, since nothing happened, but other audit operations produce audit records in the case of failure so this one might.