Hi experts,
I have a requirement where the user should be able to include the records where the due date is not populated when i check the checkbox field in the vf page.In my case that date field is named as Due_Date__c.
I have written the follwing dynamic soql code.But it is not fetching the records where the due date is not populated.Please help
 

public class PrivateEquityReport
{
   ApexPages.StandardSetController regionStandardSetController{get;set;}
   private Id privateRecordTypeId = Fund_Activity__c.SObjectType.getDescribe().getRecordTypeInfosByName().get(' Amendment').getRecordTypeId();
   public AI_PrivateEquityWeeklyTrackingReport()
   String baseQuery = 'SELECT Id,Due_Date__c,Fund__r.Name,Company__r.Name,Subject__c,Comments__c,Date_Received__c,Business_Review__c,Attorney_Review__c FROM Fund__c WHERE Team__c=\'Equity\' AND RecordTypeId =:privateRecordTypeId';

   public PrivateEquityReport()
  {
    regionStandardSetController=new ApexPages.StandardSetController(new  list<Fund__c>());
    String dueDateCheck=System.currentPageReference().getParameters().get('DueDateCheck');
    if(dueDateCheck=='true')
      isDueDate=true; 
   else
      isDueDate=false;
  }

public String  getReportText()
{
    String checkQuery = baseQuery;

     String reportFromDateVar = System.currentPageReference().getParameters().get('dFromDate');
     Date fromDateVar = null;
    if(reportFromDateVar != null)
    fromDateVar = Date.valueOf(reportFromDateVar);
    System.debug('*****From Date***'+fromDateVar );

     String reportToDateVar = System.currentPageReference().getParameters().get('dToDate');
     Date toDateVar = null;
    if(reportToDateVar != null)
    toDateVar = Date.valueOf(reportToDateVar );
     System.debug('*****To Date***'+toDateVar );

     if((fromDateVar!= null)&&(toDateVar!=null)&&(!isDueDate))
    {
      checkQuery =checkQuery +' '+'and (Due_Date__c>=:fromDateVar AND Due_Date__c<= :toDateVar)';
      checkQuery =checkQuery +' '+'and Due_Date__c=NULL';
      system.debug('************3'+checkQuery);
    }

    regionStandardSetController=new ApexPages.StandardSetController(Database.getQueryLocator(checkQuery));
    activityRecords= regionStandardSetController.getRecords();
     displayPrivateEquity ='<table><tr><td>&nbsp;</td></tr><tr><td>&nbsp;</td></tr></table>' + displayPrivateEquity ;                
     displayPrivateEquity = prepareReportSinglePagePrivateEquity(activityRecords,displayPrivateEquity );
     return  displayPrivateEquity; 
}

Thanks,
Lahari