title: The number of conditions on the keys is invalid dynamo db with node js
body: <pre><code>docClient.update({
      TableName: 'patient',
      Key: {
          "patientId": "TIGERPAT0001"
      },
      UpdateExpression: "set title = :x, name = :y",
      ExpressionAttributeNames: {
          "#name": "name"
      },
      ExpressionAttributeValues: {
          ":x": 'title value abc',
          ":y": 'name value xyz'
      }
  }, function (err, data) {
      if (err) {
          json.status = '0';
          json.result = { 'error': 'Unable to Edit Patient : ' + JSON.stringify(err) };
          res.send(json);
      } else {
          json.status = '1';
          json.result = { 'sucess': 'Patient Edited Successfully :' };
          res.send(json);
      }
  });
  </code></pre>
  
  <p>when use above code, i got res :</p>
  
  <pre><code>Unable to Edit Patient Error : `{"message":"The number of conditions on the keys is invalid",
  "code":"ValidationException", 
  "time":"2017-09-13T07:12:56.608Z",
  "requestId":"a01c707c-86b4-41a5-a1c5-92b9ea07c026",
  "statusCode":400,"retryable":false,
  "retryDelay":6.368631970657979}`
  </code></pre>
  
  <p>What do I miss / any mistake??</p>