Collections sdk always shows empty Item object when importing from JSON

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I have a json file, where I am using this json I receive from postman rest api -

{
    "info": {
        "_postman_id": "ac278c9e-d1d7-4a50-8d15-134de3de5e80",
        "name": "Types",
        "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
    },
    "item": [{
        "name": "get",
        "id": "0bf436da-794b-45c7-adf5-32f0e7a70105",
        "protocolProfileBehavior": {
            "disableBodyPruning": true
        },
        "request": {
            "method": "POST",
            "header": [],
            "body": {
                "mode": "raw",
                "raw": "{\r\n    \"userId\": {{userId}},\r\n    \"projectId\": {{projectId}}\r\n}",
                "options": {
                    "raw": {
                        "language": "json"
                    }
                }
            },
            "url": {
                "raw": "http://localhost:9090/types/get",
                "protocol": "http",
                "host": ["localhost"],
                "port": "9090",
                "path": ["types", "get"]
            }
        },
        "response": []
    }]
}

Then I am using this code to create a collection object and iterate over items -

let Collection = require('postman-collection').Collection;

let collObj = JSON.stringify(fs.readFileSync('postmanapi.json').toString());
const collection = new Collection(collObj);
console.log(collection);

No matter what I try, I always end up with a collection object which has empty item object

{"item":[],"event":[],"variable":[],"info":{"_postman_id":"f165a325-ba8a-4117-8fd3-c5e3e68369e1","schema":"https://schema.getpostman.com/json/collection/v2.1.0/collection.json"}}

How do I solve this? Thanks. Is this a version issue? I am using -
"postman-collection": "^4.1.0"