hey Guys,

I have written an Apex class and Visual Force page which searches the records from custom object. There is a field which is a multi pick list and it is a filter field. User selets the value in that field and all the records meeting the critiriea appear in the 'Results' section. This page has 3 buttons "Search", "Cancel" and "Export to CSV". I am stuck in achieveing desired code coverage. I have written a test class but it's giving me error and code coverage is only 29%. Can someone pleae help me out ? Any help will be appreciated

Here is the error message:
System.NullPointerException: Attempt to de-reference a null object
Stack Trace Class.Fetchsiteplacement.FillAggregates: line 77, column 1
Class.TestFetchsiteplacement.myUnitTest: line 49, column 1

Multi picklist filed - Device__c (It can be PC, Tablet, Mobile). Here is Apex class:

public class Fetchsiteplacement{
String devicetype;
 
   public Site_Placements__c  sp{get;set;}
    public List<Site_Placements__c > spRec{get;set;}
    public List<Site_Placements__c > spRec1{get;set;}
    public List<siteplacementwrapper> spwrapper{get;set;}
    public List<siteplacementwrapper> spwrapperexcel{get;set;}    

    public class siteplacementwrapper{
            
           
            public String Name {get;set;}
           }
        public Fetchsiteplacement(){
        sp=new Site_Placements__c ();
        spRec = new List<Site_Placements__c>();
        
        }
        
         public void FillAggregates(){
          String devicetype= '';
         string[] lststr1=sp.Device_Type__c.split(';');
            
 for (String s1: lststr1) {
                            devicetype+= '\'' + s1 + '\',';
                                }
                   devicetype= devicetype.substring (0,devicetype.length() -1);

            spwrapper=new List<siteplacementwrapper>();
            spwrapperexcel=new List<siteplacementwrapper>();
                   
             String sitePlacementQuery ='SELECT Id,Name from Site_Placements__c WHERE Device_Type__c INCLUDES (' + devicetype + ')  ';
            spRec=database.query(sitePlacementQuery);
            
            String sitePlacementQuery1 ='SELECT Id,Name  from Site_Placements__c WHERE Device_Type__c INCLUDES (' + devicetype + ')  ';
            spRec1=database.query(sitePlacementQuery1);
            
             if(spRec.size() == 0)
                {
                        Apexpages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO,''+'No records match your criteria'));
                } 
             else {
             
              for(Site_Placements__c sitePlacement:spRec){
              
               siteplacementwrapper spr=new siteplacementwrapper();
               
               
              spr.Name=sitePlacement.Name;
              spwrapper.add(spr);
              }  
             
             for(Site_Placements__c sitePlacement:spRec1){
              
              siteplacementwrapper spr=new siteplacementwrapper();
               
              spr.Name=sitePlacement.Name;
             
              spwrapperexcel.add(spr);
             
             
              }
             
             }
         }  
                
                
        public PageReference FetchExcelReport() {
        PageReference nextpage = new PageReference('/apex/RFP_Excel_Page');
return nextpage;
}
         
         public pagereference CancelSPRec(){
     
    PageReference page = new PageReference('https://c.cs30.visual.force.com/apex/SiteListPage');
    page.SetRedirect(true);
    return page;
    }}


Apex Test class:

@isTest(seeAllData=true)
private class TestFetchsiteplacement {
    
 static testMethod void myUnitTest() {
        // TO DO: implement unit test
        Account a = new Account(Name='Test Account');
      insert a;

      Publisher_Deal_Types__c pubdeal = new Publisher_Deal_Types__c ( Name = 'Test Publisher deal type', Account_Name__c = a.Id);
        
        insert pubdeal;
        
        Site_Placements__c sp = new Site_Placements__c ();
        sp.Name = 'Test site placement';
        sp.Publisher_Account_Name_clickable__c = a.Id;
        sp.Publisher_or_Vendor_Deal_Type_Name__c = pubdeal.Id;
        sp.Device_Type__c = 'PC';
        
        insert sp;
      
      PageReference ref = new PageReference('/apex/SiteListPage');
      
      Test.setCurrentPage(ref);
      
      PageReference nextpage = new PageReference('/apex/RFP_Excel_Page');
      Test.setCurrentPage(nextpage);
 
    Test.startTest();
    Fetchsiteplacement myController = new Fetchsiteplacement();
    myController.FillAggregates();
    myController.FetchExcelReport();
    myController.CancelSPRec();
    Test.stopTest();

     Site_Placements__c selectedSP = [SELECT Device_Type__c FROM Site_Placements__c WHERE Id = :sp.Id];
     System.assertEquals('PC', selectedSP.Device_Type__c);
     
 }
}