additionalProperties not working as expected in swagger

Question

I am trying to create a component in swagger in JSON for an object which has 3 properties, one of which is always a string and the other 2 properties can be of any type, i.e. string, integer, object, array, etc.

"Obj":{
"type" : "object",
"properties": {
      "X": {
          "type": "string"
        }    
   },
"additionalProperties": {}
}

But when the other 2 properties get matched to additional properties, they get stored as a key value pair instead of getting stored as it is.

Is there any other work around for this such that the other properties get stored along with "X" normally and not as a key-valaue pair? That is, is there some generic value for "type" that can be used?