Graphql Request for IDFilter gives coered Null Value Exception

[IndrajithPa]

I have a graphql query which takes IDFilter! as parameter and this works fine in the graphql editor and when i try to request from postman i am getting 

"Variable 'paths' has an invalid value: Variable 'paths' has coerced Null value for NonNull type 'IDFilter!'"

exception.

My Graphql Query

query ($expression:IDFilter!) {
internetList(
filter: {
_path: $expression
}
) {
items {
_path
}
}
}

Graphql Variables

{

   "expression":{

      "_logOp":"OR",

      "_expressions":[

         {

             "_operator": "EQUALS",

            "value":"/content/dam/sample/content-fragments/internet/internet1"

         },

         {

            "_operator": "EQUALS",

            "value":"/content/dam/sample/content-fragments/internet/internet2"

         }

      ]

   }

}