Flutter web3dart error: Invalid argument: Instance of '_BigIntImpl'

Question

I am using web3dart with flutter for calling a smart contract view function from my android application. The call errs: Invalid argument: Instance of '_BigIntImpl'. The Solidity function requires String input like so:

function getIndividualCustomer(string memory _customer) public view returns (uint256 individualSellCount,
                                                                   uint256 individualSellAmount,
                                                                   uint256 individualBuyCount,
                                                                   uint256 individualBuyAmount,
                                                                   uint256 individualTransactionsPostEntry,
                                                                   uint256 individualAccruedDividend,
                                                                   address individualPayAddress) {
        return (customers[_customer].individualSellCount,
                customers[_customer].individualSellAmount,
                customers[_customer].individualBuyCount,
                customers[_customer].individualBuyAmount,
                customers[_customer].individualTransactionsPostEntry,
                customers[_customer].individualAccruedDividend,
                customers[_customer].individualPayAddress); 

    }

The function was tested fine from Remix. Now I am integrating it with my flutter application like so:

    QuerySnapshot addressesSnapshot = await fetchDocuments();
    final contract = await fetchContract();
    for (var doc in addressesSnapshot.docs) {
      final id = (doc.data() as Map<String, dynamic>)['id'];
      final function = contract.function('getIndividualCustomer');
      List<dynamic> paramList = [];
      paramList.add(id);
            
      try {
        final result = await client.call(
          contract: contract,
          function: function,
          params: [id],
        );
        // Update the document with the returned data
        await doc.reference.update({
          'userSellCount': result[0],
          'userTotalSellAmount': result[1],
          'userBuyCount': result[2],
          'userTotalBuyAmount': result[3],
          'userTotalTransactionsPostEntry': result[4],
          'userTotalAccruedDividend': result[5],
          'userAccount': result[6],
        });
        debugPrint(
            'getIndividualCustomer call was successful for id: $id');
      } catch (e) {
        debugPrint(
            'getIndividualCustomer call failed for id: $id. Error: $e');
      }
    }
  }

The function is expected to retrieve details of input string memory _customer. In my case the input argument "id" is a UID of the form say, 9UlY5QpsmONa5bw1ZAV3yAdTwNL2. params of web3dart call is a List which take a list of input arguments. I have ensured that id is a string by checking its runtimeType and put it in a List. I have even tried with hardcoded literals. So my only argument is a string and nothing indicative of a BigInt.

However, every time I get the same error: Invalid argument: Instance of '_BigIntImpl'