title: AWS step functions and optional parameters
body: <p>I would like to have a default value for a parameter passed into a step function </p>
  
  <p>e.g., </p>
  
  <pre><code>"Parameters": {
     "foo.$": "$.foo" OR "bar" if "$.foo" not specified
  }
  </code></pre>
  
  <p>is there a way to do this natively with JSONPath or do I have to use a choice + pass state?</p>
  
  <p>I'd even settle for using choice/pass if there were a way to not break when a parameter is not specified in the input.  </p>
  
  <p>If I don't include <code>"foo": ""</code> in the input, I will get an error like <code>"JSONPath ... could not be found in the input."</code></p>