title: DynamoDB with PHP, error with update_item
body: <p>I'm trying to update a table in my DynamoDB tables using the PHP SDK. Here's the error:</p>
  
  <p>com.amazon.coral.service#SerializationException
  Start of list found where not expected</p>
  
  <p>I'm guessing there is something wrong with the formatting of my array. I'm using this <a href="http://docs.amazonwebservices.com/AWSSDKforPHP/latest/#m=AmazonDynamoDB/update_item" rel="nofollow">documentation</a> for reference. </p>
  
  <p><strong>The Array I'm sending:</strong></p>
  
  <pre><code>array(3) {
    ["TableName"]=&gt;
    string(7) "teacher"
    ["Key"]=&gt;
    array(1) {
      ["HashKeyElement"]=&gt;
      array(1) {
        ["S"]=&gt;
        string(36) "97770A6A-EF06-AF4A-3E30-87DAC0237F6D"
      }
    }
    ["AttributeUpdates"]=&gt;
    array(1) {
      [0]=&gt;
      array(2) {
        ["population"]=&gt;
        array(1) {
          ["Action"]=&gt;
          string(3) "ADD"
        }
        ["Value"]=&gt;
        array(1) {
          ["SS"]=&gt;
          array(1) {
            [0]=&gt;
            string(36) "97770A6A-EF06-AF4A-3E30-87DAC0237F6D"
          }
        }
      }
    }
  }
  </code></pre>