Mountebank predicates doesn't check headers

I have below code and looks like it is not checking headers as a predicate.

{
  "responses": [
    {
      "inject": "<%- stringify(filename, 'Scripts/MyDept/CutOffTime.ejs') %>"
    }
  ],
  "predicates": [
    {
      "matches": {
        "method": "GET",
        "path": "/cutoff-times",
        "query": {
          "country": "\\w+"
        },
        "headers": {
          "X-CLIENT-ID": "^[ A-Za-z0-9]*$"
        }
      }
    }
  ]
}

Strangely, when I pass @ as the value to header X-CLIENT-ID it validate and shows the message as no predicate match. Because it is not part of the regex.

Identified the issue,

Basically if you need have multiple predicates need to merge them as below,(using and / or)

{
  "responses": [
    {
      "inject": "<%- stringify(filename, 'Scripts/MyDept/CutOffTime.ejs') %>"
    }
  ],
  "predicates": [
        {
          "and": [
            {
              "exists": {
                "headers": {
                  "X-CLIENT-ID": true,
                  }
              }
            },
            {
              "matches": {
                "method": "GET",
                "path": "/cutoff-times",
                "headers": {
                  "X-CLIENT-ID": "^[ A-Za-z0-9]*$"
                },
                "query": {
                  "country": "\\w+"
                  }
              }
            }
          ]
        }
      ]
  }

Mountebank site

Further matches predicate doesn't check the existence (e.g. header existence)