title: How to search resources without a specific tag
body: <p>I'm using <a href="https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/EC2.html" rel="nofollow noreferrer">AWS Javascript SDK</a> to query my cloud infrastructure through AWS API.</p>
  
  <p>I can query resources by tag specifying a key=value pair in the filter, such as "Environment=Production". What I cannot find is how to query for null valued tags or non-existent tags. For example, I want to query for all EC2 instances that do not have a certain tag defined, let's say, all EC2 instances that do not have an "Environment" tag.</p>
  
  <p>Is that possible with the SDK?</p>