From 6134722b550a5a27b3e1018fb7ed6690e5fec984 Mon Sep 17 00:00:00 2001
From: Reed Passaretti <reed@Reeds-MacBook-Air.local>
Date: Mon, 15 Mar 2021 10:46:17 -0400
Subject: [PATCH] Empty beans are now preserved through serialization and
 deserialization

---
 .../bugfix-AmazonDynamoDBEnhanced-dbd1477.json            | 6 ++++++
 .../dynamodb/mapper/StaticImmutableTableSchema.java       | 8 ++------
 .../dynamodb/mapper/StaticImmutableTableSchemaTest.java   | 2 +-
 .../enhanced/dynamodb/mapper/StaticTableSchemaTest.java   | 2 +-
 4 files changed, 10 insertions(+), 8 deletions(-)
 create mode 100644 .changes/next-release/bugfix-AmazonDynamoDBEnhanced-dbd1477.json

diff --git a/.changes/next-release/bugfix-AmazonDynamoDBEnhanced-dbd1477.json b/.changes/next-release/bugfix-AmazonDynamoDBEnhanced-dbd1477.json
new file mode 100644
index 000000000000..0bed6050bf34
--- /dev/null
+++ b/.changes/next-release/bugfix-AmazonDynamoDBEnhanced-dbd1477.json
@@ -0,0 +1,6 @@
+{
+    "category": "Amazon DynamoDB Enhanced", 
+    "contributor": "reed53", 
+    "type": "bugfix", 
+    "description": "Empty beans are now preserved through serialization and deserialization"
+}
diff --git a/services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchema.java b/services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchema.java
index 896b4901b59b..cd4ebe1b8d82 100644
--- a/services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchema.java
+++ b/services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchema.java
@@ -439,8 +439,7 @@ public StaticTableMetadata tableMetadata() {
 
     @Override
     public T mapToItem(Map<String, AttributeValue> attributeMap) {
-        // Lazily instantiate the builder once we have an attribute to write
-        B builder = null;
+        B builder = constructNewBuilder();
         Map<FlattenedMapper<T, B, ?>, Map<String, AttributeValue>> flattenedAttributeValuesMap = new LinkedHashMap<>();
         
         for (Map.Entry<String, AttributeValue> entry : attributeMap.entrySet()) {
@@ -451,9 +450,6 @@ public T mapToItem(Map<String, AttributeValue> attributeMap) {
                 ResolvedImmutableAttribute<T, B> attributeMapper = indexedMappers.get(key);
 
                 if (attributeMapper != null) {
-                    if (builder == null) {
-                        builder = constructNewBuilder();
-                    }
 
                     attributeMapper.updateItemMethod().accept(builder, value);
                 } else {
@@ -479,7 +475,7 @@ public T mapToItem(Map<String, AttributeValue> attributeMap) {
             builder = entry.getKey().mapToItem(builder, this::constructNewBuilder, entry.getValue());
         }
         
-        return builder == null ? null : buildItemFunction.apply(builder);
+        return buildItemFunction.apply(builder);
     }
 
     @Override
diff --git a/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchemaTest.java b/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchemaTest.java
index 177384e358bb..511964dce3bb 100644
--- a/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchemaTest.java
+++ b/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticImmutableTableSchemaTest.java
@@ -1499,7 +1499,7 @@ private <R> void verifyNullAttribute(EnhancedType<R> attributeType,
         assertThat(resultMap, is(expectedMap));
 
         FakeMappedItem resultItem = tableSchema.mapToItem(expectedMap);
-        assertThat(resultItem, is(nullValue()));
+        assertThat(resultItem, is(FakeMappedItem.builder().build()));
     }
 
     private <R> void verifyNullableAttribute(EnhancedType<R> attributeType,
diff --git a/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticTableSchemaTest.java b/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticTableSchemaTest.java
index fc43da907b08..d366b759203b 100644
--- a/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticTableSchemaTest.java
+++ b/services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/mapper/StaticTableSchemaTest.java
@@ -1517,7 +1517,7 @@ private <R> void verifyNullAttribute(EnhancedType<R> attributeType,
         assertThat(resultMap, is(expectedMap));
 
         FakeMappedItem resultItem = tableSchema.mapToItem(expectedMap);
-        assertThat(resultItem, is(nullValue()));
+        assertThat(resultItem, is(FakeMappedItem.builder().build()));
     }
 
     private <R> void verifyNullableAttribute(EnhancedType<R> attributeType,