title: DynamoDB Update - ExpressionAttributeNames can only be specified when using expressions
body: <p>I need another set of eyes on this. For the life of me I see no issues with this parameter set, used for Dynamo DocumentClient, <strong>update</strong> method - (here: <a href="https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html#update-property" rel="noreferrer">https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html#update-property</a> ). </p>
  
  <pre><code>{
      TableName: "mygame-dev",
      Key: { pk: "09d017aa-cbf7-42ce-be6a-a94ecb58f9a7", sk: "GAME" },
      ExpressionAttributeNames: { "#GAMELASTUPDATED": "gameLastUpdated", "#GAMETITLE": "gameTitle" },
      ExpressionAttributeValues: { ":gamelastupdated": 1556376010704, ":gametitle": "test title 1" },
      UpdateExpression: "SET #GAMELASTUPDATED = :gamelastupdated, #GAMETITLE = :gametitle",
      ReturnValues: "ALL_NEW"
  };
  </code></pre>
  
  <p>Error: </p>
  
  <blockquote>
    <p>ValidationException: ExpressionAttributeNames can only be specified
    when using expressions</p>
  </blockquote>
  
  <p>Any thoughts? </p>