Does Dynalite support atomic counters

[Fred Hart]

Does Dynalite support atomic counters? I am getting an error when calling the update using the DocumentClient interface. _uc is supposed to be an update counter for the record, but I get an error. Sets can contain string, number, or binary values. It seems to be treating _uc as a set and not an integer.

          "params": {
            "ExpressionAttributeNames": {
              "#_uc": "_uc",
              "#a": "Email",
            },
            "ExpressionAttributeValues": {
              ":_uc": 1,
              ":a": "[e-mail]",
            },
            "Key": {
              "transaction_id": "subscriptionNumber:1234"
            },
            "ReturnValues": "ALL_NEW",
            "TableName": "mytable",
            "UpdateExpression": "set #a=:a add #_uc :_uc"
          }
        }