Based on the API doc, we shouldn't have `AttributeValueList` in this case:

http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Scan.html#DDB-Scan-request-ScanFilter

"*AttributeValueList - One or more values to evaluate against the supplied attribute. This list contains exactly one value, except for a BETWEEN or IN comparison, in which case the list contains two values.*"

The previous code was definitely buggy, but can you add a unit test case to make sure your new code works?