fix(dynamodb): reject empty sets and non-string map keys in TypeSerializer

boto3/dynamodb/types.py

@@ -189,7 +189,7 @@ def _is_set(self, value):
         return False
 
     def _is_type_set(self, value, type_validator):
-        if self._is_set(value):
+        if self._is_set(value) and len(value) > 0:
             if False not in map(type_validator, value):
                 return True
         return False
@@ -237,6 +237,11 @@ def _serialize_l(self, value):
         return [self.serialize(v) for v in value]
 
     def _serialize_m(self, value):
+        for k in value:
+            if not isinstance(k, str):
+                raise TypeError(
+                    f'Map keys must be strings, got {type(k).__name__}: {k!r}'
+                )
         return {k: self.serialize(v) for k, v in value.items()}
 
 

tests/unit/dynamodb/test_types.py

@@ -143,6 +143,14 @@ def test_serialize_map(self):
             'M': {'foo': {'S': 'bar'}, 'baz': {'M': {'biz': {'N': '1'}}}}
         }
 
+    def test_serialize_empty_set_raises_error(self):
+        with pytest.raises(TypeError, match=r'Unsupported type'):
+            self.serializer.serialize(set())
+
+    def test_serialize_map_with_non_string_key_raises_error(self):
+        with pytest.raises(TypeError, match=r'Map keys must be strings'):
+            self.serializer.serialize({1: 'a'})
+
 
 class TestDeserializer(unittest.TestCase):
     def setUp(self):