Not able to trace the following code in test class

Question

Here I have a controller and test class, but I am not sure why I am getting the following error.

Error Message: System.NullPointerException: Argument cannot be null.

Stack Trace Class.CustomProductSelectionController.: line 36, column 1 Class.TestCustomProductSelectionController.myUnitTest: line 37, column 1

APEX CLASS

public CustomProductSelectionController(ApexPages.StandardController Controller){
    Product2Id = ApexPages.currentPage().getParameters().get('Product2Id');
    opp = new Opportunity();
    opp.Id = Apexpages.currentPage().getParameters().get('Id');
    opp.LID__LinkedIn_Company_Id__c = Apexpages.currentPage().getParameters().get('oppLID');
    opp.Name = Apexpages.currentPage().getParameters().get('oppName');
    opp.Accountid = Apexpages.currentPage().getParameters().get('oppAccountid');
    /* Below is my Line 36 */
    opp.CloseDate = Date.Parse(Apexpages.currentPage().getParameters().get('oppCloseDate'));
    opp.PrimaryTechnologyArchitect__c = Apexpages.currentPage().getParameters().get('oppPrimaryTech');
    opp.StageName = Apexpages.currentPage().getParameters().get('oppStageName');
    opp.Probability = Decimal.valueOf(Apexpages.currentPage().getParameters().get('oppProbability'));
    opp.Type = Apexpages.currentPage().getParameters().get('oppType');
    opp.WinLoss__c = Apexpages.currentPage().getParameters().get('oppWinLoss__c');
    opp.LeadSource = Apexpages.currentPage().getParameters().get('oppLeadSource');
    opp.Assessment__c = Apexpages.currentPage().getParameters().get('oppAssessment__c');
    opp.Budget__c = Apexpages.currentPage().getParameters().get('oppBudget');
    opp.ContractNumber__c = Apexpages.currentPage().getParameters().get('oppContractNumber');
    opp.Competition__c = Apexpages.currentPage().getParameters().get('oppCompetition');
    opp.Competition2__c = Apexpages.currentPage().getParameters().get('oppCompetition2');
    opp.Competition3__c = Apexpages.currentPage().getParameters().get('oppCompetition3');
    opp.SOW_Nbr__c = Apexpages.currentPage().getParameters().get('oppSOW');
    opp.BIG_Sow_Number__c = Apexpages.currentPage().getParameters().get('oppSowNumber');
    oppId = Apexpages.currentPage().getParameters().get('oppId');

    checkSelect = Apexpages.currentPage().getParameters().get('oppPrimaryTech');
    sowVal = Apexpages.currentPage().getParameters().get('oppSOW');

    wrappProductList = new List<wrappProduct>();
    product = new Product2[]{};
    AddProduct();
}

APEX TEST CLASS

@isTest
Public class TestCustomProductSelectionController{

    Private static testMethod void myUnitTest() {

        Account acc = new Account();
        acc.Name = 'Test Account';
        insert acc;

        Opportunity opp = new Opportunity();
        opp.Name = 'Test Opportunity';
        opp.CloseDate = date.today();
        opp.StageName = 'Prospecting';
        opp.PrimaryTechnologyArchitect__c = 'Ryan';
        opp.AccountId = acc.Id;
        opp.LID__LinkedIn_Company_Id__c = '123';
        opp.Probability = 10;
        opp.Type = 'New Buisness';
        opp.WinLoss__c = '10';
        opp.LeadSource = 'EMC';
        opp.Assessment__c = 'Yes';
        opp.Budget__c = '500';
        opp.ContractNumber__c = '10';
        opp.Competition__c = 'CNT';
        opp.Competition2__c = 'CSC';
        opp.Competition3__c = 'ICP';
        opp.SOW_Nbr__c = '2';
        opp.BIG_Sow_Number__c = '1';
        insert opp;

        Product2 p = new Product2();
        p.Name = 'Test Product';
        p.Manufacturer__c = 'CDI Consulting';
        insert p;

        ApexPages.StandardController sc = new ApexPages.StandardController(opp);
        /* Below is my Line 37 */
        CustomProductSelectionController controller = new CustomProductSelectionController(sc);

        CustomProductSelectionController.wrappProduct wrapper = new CustomProductSelectionController.wrappProduct();

        controller.oppId = Apexpages.currentPage().getParameters().put('oppId', opp.Id);
        controller.Product2Id = ApexPages.currentPage().getParameters().put('Product2Id', p.Id);
        controller.opp.Id = Apexpages.currentPage().getParameters().put('Id', opp.Id);
        controller.opp.LID__LinkedIn_Company_Id__c = Apexpages.currentPage().getParameters().put('oppLID', opp.LID__LinkedIn_Company_Id__c);
        controller.opp.Name = Apexpages.currentPage().getParameters().put('oppName',opp.Name);
        controller.opp.Accountid = Apexpages.currentPage().getParameters().put('oppAccountid',opp.AccountId);
        controller.opp.CloseDate =  Apexpages.currentPage().getParameters().put('oppCloseDate', String.ValueOf(opp.CloseDate));
        controller.opp.PrimaryTechnologyArchitect__c = Apexpages.currentPage().getParameters().put('oppPrimaryTech',opp.PrimaryTechnologyArchitect__c);
        controller.opp.StageName = Apexpages.currentPage().getParameters().put('oppStageName',opp.StageName);
        //controller.opp.Probability = Apexpages.currentPage().getParameters().put('oppProbability', opp.Probability);
        controller.opp.Type = Apexpages.currentPage().getParameters().put('oppType',opp.Type);
        controller.opp.WinLoss__c = Apexpages.currentPage().getParameters().put('oppWinLoss__c',opp.WinLoss__c);
        controller.opp.LeadSource = Apexpages.currentPage().getParameters().put('oppLeadSource',opp.LeadSource);
        controller.opp.Assessment__c = Apexpages.currentPage().getParameters().put('oppAssessment__c',opp.Assessment__c);
        controller.opp.Budget__c = Apexpages.currentPage().getParameters().put('oppBudget',opp.Budget__c);
        controller.opp.ContractNumber__c = Apexpages.currentPage().getParameters().put('oppContractNumber',opp.ContractNumber__c);
        controller.opp.Competition__c = Apexpages.currentPage().getParameters().put('oppCompetition',opp.Competition__c);
        controller.opp.Competition2__c = Apexpages.currentPage().getParameters().put('oppCompetition2',opp.Competition2__c);
        controller.opp.Competition3__c = Apexpages.currentPage().getParameters().put('oppCompetition3',opp.Competition3__c);
        controller.opp.SOW_Nbr__c = Apexpages.currentPage().getParameters().put('oppSOW',opp.SOW_Nbr__c);
        controller.opp.BIG_Sow_Number__c = Apexpages.currentPage().getParameters().put('oppSowNumber',opp.BIG_Sow_Number__c);
        //controller.checkSelect = Apexpages.currentPage().getParameters().put('oppPrimaryTech',opp.IsPrivate);
        controller.sowVal = Apexpages.currentPage().getParameters().put('oppSOW',opp.BIG_Sow_Number__c);
        controller.AddProduct();
        controller.delWrapper();
        controller.SaveProduct();
        controller.retrieveProductInfo();
    }
}

Answer 1

The problem is that you are accessing the oppCloseDate parameter from the current page without assigning it, hence returning a null value. Date.parse() function can not take a null value as input.

You need to put the page parameters before calling the CustomProductSelectionController constructor.

    ApexPages.StandardController sc = new ApexPages.StandardController(opp);
    /*Put the page parameters here*/
    CustomProductSelectionController controller = new CustomProductSelectionController(sc);

Another problem I can see that you haven't set your page reference in your test class.

Test.setCurrentPage(Page.YourPageName);

Use it before initiating the standard controller to set your test method in perspective of your visualforce page.

Answer 2

If I understood it correct, your line number 36 is:

opp.CloseDate = Date.Parse(Apexpages.currentPage().getParameters().get('oppCloseDate'));

If yes, then looks like that you have to add one more line to your test class, where you need to set the oppCloseDate parameter as well.

Apexpages.currentPage().getParameters().put('oppCloseDate ',opp.closeDate);