Failed to evaluate transaction: TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string or an instance of Buffer or URL

I want to query an asset on hyper ledger fabric blockchain. I have defined a function queryCar for it. Car is an asset on the blockchain with four/five different properties, like model, color, etc.(I have copied the chaincode directly from the fabric sample GitHub repo) I'm using fabric-network along with fabric-ca-client for building my SDK in nodejs. I am getting this error :

Failed to evaluate transaction: TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string or an instance of Buffer or URL. Received null

and this as response when I call the API for querycar

{
    "result": "The \"path\" argument must be of type string or an instance of Buffer or URL. Received null",
    "error": null,
    "errorData": null
}

Node js API for query function:

app.get('/channels/:channelName/chaincodes/:chaincodeName', async function (req, res) {
    try {
        logger.debug('==================== QUERY BY CHAINCODE ==================');

        var channelName = req.params.channelName;
        var chaincodeName = req.params.chaincodeName;
        console.log(`chaincode name is :${chaincodeName}`)
        let args = req.query.args;
        let fcn = req.query.fcn;
        let peer = req.query.peer;

        if (!chaincodeName) {
            res.json(getErrorMessage('\'chaincodeName\''));
            return;
        }
        if (!channelName) {
            res.json(getErrorMessage('\'channelName\''));
            return;
        }
        if (!fcn) {
            res.json(getErrorMessage('\'fcn\''));
            return;
        }
        if (!args) {
            res.json(getErrorMessage('\'args\''));
            return;
        }
        console.log('args==========', args);
        args = args.replace(/'/g, '"');
        args = JSON.parse(args);
        logger.debug(args);

        let message = await query.query(channelName, chaincodeName, args, fcn, req.username, req.orgname);

        const response_payload = {
            result: message,
            error: null,
            errorData: null
        }

        res.send(response_payload);
    } catch (error) {
        const response_payload = {
            result: null,
            error: error.name,
            errorData: error.message
        }
        res.send(response_payload)
    }
});

Helper query blockchain function

const query = async (channelName, chaincodeName, args, fcn, username, org_name) => {

    try {

        const ccp = await helper.getCCP(org_name) //JSON.parse(ccpJSON);

        // Create a new file system based wallet for managing identities.
        const walletPath = await helper.getWalletPath(org_name) //.join(process.cwd(), 'wallet');
        const wallet = await Wallets.newFileSystemWallet(walletPath);
        console.log(`Wallet path: ${walletPath}`);

        // Check to see if we've already enrolled the user.
        let identity = await wallet.get(username);
        if (!identity) {
            console.log(`An identity for the user ${username} does not exist in the wallet, so registering user`);
            await helper.getRegisteredUser(username, org_name, true)
            identity = await wallet.get(username);
            console.log('Run the registerUser.js application before retrying');
            return;
        }

        // Create a new gateway for connecting to our peer node.
        const gateway = new Gateway();
        await gateway.connect(ccp, {
            wallet, identity: username, discovery: { enabled: true, asLocalhost: true }
        });

        // Get the network (channel) our contract is deployed to.
        const network = await gateway.getNetwork(channelName);

        // Get the contract from the network.
        const contract = network.getContract(chaincodeName);
        let result;

        switch (fcn) {
            case "queryCar":
                console.log("=============")
                result = await contract.evaluateTransaction('SmartContract:'+fcn, args[0]);
                break;
            case "GetHistoryForAsset":
            case "GetCarById":
                console.log("=============")
                result = await contract.evaluateTransaction('SmartContract:'+fcn, args[0]);
                break;
            default:
                break;
        }

        console.log(result)
        console.log(`Transaction has been evaluated, result is: ${result.toString()}`);

        result = JSON.parse(result.toString());
        return result
    } catch (error) {
        console.error(`Failed to evaluate transaction: ${error}`);
        return error.message

    }
}