From 44310b5e0eb871461583eefcb27c62160713b98d Mon Sep 17 00:00:00 2001
From: Bert Blommers <info@bertblommers.nl>
Date: Sat, 11 May 2024 20:09:14 +0000
Subject: [PATCH] DynamoDB: update_item() now throws the appriopriate exception
 when adding an empty set (#7684)

---
 moto/dynamodb/parsing/executors.py            |  5 ++
 .../test_dynamodb_update_expressions.py       | 47 +++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/moto/dynamodb/parsing/executors.py b/moto/dynamodb/parsing/executors.py
index b6a7c6eeff70..23aac7d6d9e1 100644
--- a/moto/dynamodb/parsing/executors.py
+++ b/moto/dynamodb/parsing/executors.py
@@ -4,6 +4,7 @@
 from moto.dynamodb.exceptions import (
     IncorrectDataType,
     IncorrectOperandType,
+    MockValidationException,
     ProvidedKeyDoesNotExist,
 )
 from moto.dynamodb.models.dynamo_type import (
@@ -226,6 +227,10 @@ def execute(self, item: Item) -> None:
         value_to_add = self.get_action_value()
         if isinstance(value_to_add, DynamoType):
             if value_to_add.is_set():
+                if len(value_to_add.value) == 0:
+                    raise MockValidationException(
+                        "ExpressionAttributeValues contains invalid value: One or more parameter values were invalid: An string set  may not be empty"
+                    )
                 try:
                     current_string_set = self.get_item_at_end_of_path(item)
                 except ProvidedKeyDoesNotExist:
diff --git a/tests/test_dynamodb/test_dynamodb_update_expressions.py b/tests/test_dynamodb/test_dynamodb_update_expressions.py
index d891f75d842d..5115e7168261 100644
--- a/tests/test_dynamodb/test_dynamodb_update_expressions.py
+++ b/tests/test_dynamodb/test_dynamodb_update_expressions.py
@@ -2,6 +2,7 @@
 
 import boto3
 import pytest
+from botocore.exceptions import ClientError
 
 from . import dynamodb_aws_verified
 
@@ -140,3 +141,49 @@ def test_delete_non_existing_item(table_name=None):
         ReturnValues="ALL_NEW",
     )
     assert table.get_item(Key={"pk": name})["Item"] == {"pk": "name"}
+
+
+@pytest.mark.aws_verified
+@dynamodb_aws_verified()
+def test_update_item_add_empty_set(table_name=None):
+    dynamodb = boto3.client("dynamodb", "us-east-1")
+
+    # Add to non-existing attribute
+    dynamodb.put_item(TableName=table_name, Item={"pk": {"S": "foo"}})
+    with pytest.raises(ClientError) as exc:
+        dynamodb.update_item(
+            TableName=table_name,
+            Key={"pk": {"S": "foo"}},
+            UpdateExpression="ADD stringset :emptySet",
+            ExpressionAttributeValues={":emptySet": {"SS": ()}},
+        )
+    err = exc.value.response["Error"]
+    assert err["Code"] == "ValidationException"
+    assert (
+        err["Message"]
+        == "ExpressionAttributeValues contains invalid value: One or more parameter values were invalid: An string set  may not be empty"
+    )
+
+    assert dynamodb.scan(TableName=table_name)["Items"] == [{"pk": {"S": "foo"}}]
+
+    # Still not allowed when the attribute exists
+    dynamodb.put_item(
+        TableName=table_name, Item={"pk": {"S": "foo"}, "stringset": {"SS": ("item1",)}}
+    )
+    with pytest.raises(ClientError) as exc:
+        dynamodb.update_item(
+            TableName=table_name,
+            Key={"pk": {"S": "foo"}},
+            UpdateExpression="ADD stringset :emptySet",
+            ExpressionAttributeValues={":emptySet": {"SS": ()}},
+        )
+    err = exc.value.response["Error"]
+    assert err["Code"] == "ValidationException"
+    assert (
+        err["Message"]
+        == "ExpressionAttributeValues contains invalid value: One or more parameter values were invalid: An string set  may not be empty"
+    )
+
+    assert dynamodb.scan(TableName=table_name)["Items"] == [
+        {"pk": {"S": "foo"}, "stringset": {"SS": ["item1"]}}
+    ]