title: Updating a list in DynamoDB
body: <p>I have tried a number of solutions give here in SO but having trouble with one validation error:
  This is my table:</p>
  
  <pre><code>var params = {
      AttributeDefinitions: [
          {
              AttributeName: 'USER_AUTH_ID',
              AttributeType: 'N'
          },
          {
              AttributeName: 'EMAIL',
              AttributeType: 'S'
          }
      ],
      KeySchema: [
          {
              AttributeName: 'EMAIL',
              KeyType: 'HASH'
          },
          {
              AttributeName: 'USER_AUTH_ID',
              KeyType: 'RANGE'
          }
      ],
      ProvisionedThroughput: {
          ReadCapacityUnits: 1,
          WriteCapacityUnits: 1
      },
      TableName: tableName,
      StreamSpecification: {
          StreamEnabled: false
      }
  };
  </code></pre>
  
  <p>I have successfully created items using putItem, but having trouble appending to a list:</p>
  
  <p>This is my item to update:</p>
  
  <pre><code>var paramUpdateItem = {
      TableName: tableName,
      Key: {
          'EMAIL' : {S: 'MyEmail@email.com'}
      },
      UpdateExpression: "SET #Y = list_append(#Y,:y)",
      ExpressionAttributeNames: {
          "#Y" : "COMMENT_HISTORY"
      },
      ExpressionAttributeValues: {
          ":y" : [commentToAdd]
      }
  }
  </code></pre>
  
  <p>;</p>
  
  <p>And I update with <code>updateItem</code>.</p>
  
  <p>I keep getting this error:</p>
  
  <blockquote>
    <p>null: Error: Unexpected key '0' found in
    params.ExpressionAttributeValues[':y']</p>
  </blockquote>
  
  <p>I read in another question this is due to tabs, but I have tried to fix it but still getting this error.</p>
  
  <p>Any help.
  Thank you.</p>