title: list_append causing duplicates in Map. if list_append called for for existing keys in DynamoDB
body: <p>In following code in java I am trying to append an item "test.com" to a Map field named "daily". When I run this code it just adds a dulplicate key to the Map.</p>
  
  <pre><code>Map&lt;String,String&gt; atrVal = new HashMap&lt;String,String&gt;();
                  atrVal.put("test.com", json);
                  UpdateItemSpec updateItemSpec = new UpdateItemSpec()
                          .withPrimaryKey("id", Id)
                          .withUpdateExpression("set daily = list_append(daily , :r)")
                          .withConditionExpression("attribute_not_exists (daily.#k1)")
                          .withValueMap(new ValueMap()
                                  .withList(":r", Arrays.asList(atrVal))
  
                                  )
                          .withNameMap(new NameMap()
                                  .with("#k1", "test.com"));
                  table.updateItem(updateItemSpec);
  </code></pre>
  
  <p><code>attribute_not_exists</code> should be preventing it from doing that. Any ideas why its not working.</p>
  
  <p><a href="https://i.stack.imgur.com/0EqUL.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0EqUL.jpg" alt=""></a></p>