Add null check on the input of DynamodbAttributeValueTransformer.toAttributeValueMapV1 (#254)

Co-authored-by: Yongrui Gao <yongru@amazon.com>

Author: yongruigao

aws-lambda-java-events-sdk-transformer/src/main/java/com/amazonaws/services/lambda/runtime/events/transformers/v1/dynamodb/DynamodbAttributeValueTransformer.java

@@ -63,6 +63,10 @@ public static AttributeValue toAttributeValueV1(final com.amazonaws.services.lam
     public static Map<String, AttributeValue> toAttributeValueMapV1(
             final Map<String, com.amazonaws.services.lambda.runtime.events.models.dynamodb.AttributeValue> attributeValueMap
     ) {
+        if (attributeValueMap == null) {
+            return null;
+        }
+
         return attributeValueMap
                 .entrySet()
                 .stream()

aws-lambda-java-events-sdk-transformer/src/test/java/com/amazonaws/services/lambda/runtime/events/transformers/v1/dynamodb/DynamodbAttributeValueTransformerTest.java

@@ -313,4 +313,9 @@ public void testToAttributeValueV1_EmptyV1ObjectWhenEmpty_L() {
                 DynamodbAttributeValueTransformer.toAttributeValueV1(new AttributeValue().withL(Collections.emptyList())));
     }
 
+    @Test
+    public void testToAttributeValueMapV1_NullV1AttributeValueMapWhenNullEventAttributeValueMap() {
+        Assertions.assertNull(DynamodbAttributeValueTransformer.toAttributeValueMapV1(null));
+    }
+
 }