Fix failure of scan() after has_item()

Fixes #731

moto/dynamodb/responses.py

@@ -278,7 +278,7 @@ class DynamoHandler(BaseResponse):
 
         result = {
             "Count": len(items),
-            "Items": [item.attrs for item in items],
+            "Items": [item.attrs for item in items if item],
             "ConsumedCapacityUnits": 1,
             "ScannedCount": scanned_count
         }

tests/test_dynamodb/test_dynamodb_table_with_range_key.py

@@ -419,6 +419,17 @@ def test_scan_with_undeclared_table():
     ).should.throw(DynamoDBResponseError)
 
 
+@mock_dynamodb
+def test_scan_after_has_item():
+    conn = boto.connect_dynamodb()
+    table = create_table(conn)
+    list(table.scan()).should.equal([])
+
+    table.has_item(hash_key='the-key', range_key='123')
+
+    list(table.scan()).should.equal([])
+
+
 @mock_dynamodb
 def test_write_batch():
     conn = boto.connect_dynamodb()

tests/test_dynamodb/test_dynamodb_table_without_range_key.py

@@ -335,6 +335,17 @@ def test_scan_with_undeclared_table():
     ).should.throw(DynamoDBResponseError)
 
 
+@mock_dynamodb
+def test_scan_after_has_item():
+    conn = boto.connect_dynamodb()
+    table = create_table(conn)
+    list(table.scan()).should.equal([])
+
+    table.has_item('the-key')
+
+    list(table.scan()).should.equal([])
+
+
 @mock_dynamodb
 def test_write_batch():
     conn = boto.connect_dynamodb()