title: NUMBER_VALUE cannot be converted to String when updating Item
body: <p>I have this strange issue with DynamoDB where I cannot seem to update an item.</p>
  <p>Here is my command:</p>
  <pre><code>TableName: 'UserTable',
  Key: { UID: { S: 'h4XJj3YRxZiF7TDcGkxAhc' } },
  UpdateExpression: 'SET numRatings = :numRatings',
  ExpressionAttributeValues: { ':numRatings': { N: 336 } },
  ReturnValues: 'UPDATED_NEW'
  </code></pre>
  <p>I have verified that the table is correct, and that the key of the table UID does indeed have the hash <code>h4XJj3YRxZiF7TDcGkxAhc</code> as a value. <code>numRatings</code> currently is equal to 1.</p>
  <p>Here's my code:</p>
  <pre><code>  const params = {
      TableName: process.env.USER_TABLE_NAME!,
      Key: {
        UID: {
          S: UID
        }
      },
      UpdateExpression: 'SET numRatings = :numRatings',
      ExpressionAttributeValues: {
        ':numRatings': { N: numRatings } as unknown as AttributeValue
      },
      ReturnValues: 'UPDATED_NEW'
    } as UpdateItemCommandInput;
  
    try {
      const result = await dbClient.send(new UpdateItemCommand(params));
  ...
  </code></pre>
  <p>Yet I get this error: <code>NUMBER_VALUE cannot be converted to String</code> maybe I am blind but I cannot see where this conversion could be taking place.</p>
  <p>I am using TypeScript and AWS-SDK 3.54.0</p>
  <p>If anyone is able to point out what I am doing wrong I would greatly appreciate it.</p>
  <p><a href="https://i.stack.imgur.com/rzlAL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rzlAL.png" alt="Item" /></a></p>