Error: DynamoDB string set may not be empty

“String set may not be empty” means a set with no members reached the serializer or service. A String Set is different from an empty String or an empty List, both of which can be valid non-key values. Fix the collection representation before sending it.

To clear an existing set without replacing the item, remove the attribute:

import boto3

table = boto3.resource("dynamodb", region_name="us-east-1").Table("Orders")
table.update_item(
    Key={"id": "123"},
    UpdateExpression="REMOVE #tags",
    ConditionExpression="attribute_exists(#id)",
    ExpressionAttributeNames={"#tags": "tags", "#id": "id"},
)

The condition prevents this cleanup from creating a new item at an absent key. If an explicit empty collection must remain present, store a List and update readers to expect it. For new items, omit optional empty sets. Check nested values too; neither adding a placeholder member nor changing IAM permissions addresses the data-model problem.

See collection types and AWS documentation.