Hi All

System.NullPointerException: Attempt to de-reference a null object

Class.FConnect.SelectedProductsunderservice.Add: line 78, column 1

<apex:page controller="SelectedProductsunderservice">
<apex:form >
<apex:pageBlock >
<apex:pageBlockButtons id="id">
<apex:commandButton value=" Add " action="{!Add}" reRender="id"/>
<apex:commandButton value="Cancel" action="{!cancel}" reRender="id"/>
</apex:pageBlockButtons>
<apex:pageMessages ></apex:pageMessages>
<apex:pageBlockTable value="{!ProductsUnderService}" var="ip" id="table">
<apex:column >
<apex:inputCheckbox value="{!ip.selected}"/>
</apex:column> 

<apex:column value="{!ip.con.Name}"/>
<apex:column value="{!ip.con.Products__c}"/>
<apex:column value="{!ip.con.Description__c}"/>
<apex:column value="{!ip.con.Serial_ID__c}"/>
<apex:column value="{!ip.con.Asset_Tag__c}"/>
<apex:column value="{!ip.con.Quantity__c}"/>
<apex:column value="{!ip.con.Customer__c}"/>

</apex:pageBlockTable>
</apex:pageBlock>

</apex:form> 
</apex:page>

public with sharing class SelectedProductsunderservice 
{
public String AgreementLineId;
public String Customer;
public String customerName;
Public List<Products__c> Products;
Public List<Product__c> customProducts;
public List<ProductsUnderService> ProductsUnderServiceList{get;set;}
List<Id> proIds = new List<Id>();
List<Id> iprodIds = new List<Id>();

public SelectedProductsunderservice ()
{
customProducts = new List<Product__c>();
AgreementLineId=apexpages.currentpage().getparameters().get('Agreement_Line');
Agreement_Line__c al=[select id,Agreement__r.Customer__r.name from Agreement_Line__c where id=:AgreementLineId];
Customer=al.Agreement__r.Customer__c;
customerName=al.Agreement__r.Customer__r.name;

Products = [SELECT id,name ,Agreement_Line__c,Products_ID__c FROM Products__c WHERE Agreement_Line__c=:al.id ];

for(Products__c pro : Products)
{
proIds.add(pro.Products_Id__c);
}

customProducts = [SELECT Id, Name FROM Product__c WHERE Id IN :proIds];
}

public List<ProductsUnderService> getProductsUnderService()
{
ProductsUnderServiceList=new List<ProductsUnderService> ();
List<Installed_Products__c> iproducts = [select Name,
Description__c,
Serial_ID__c,
Asset_Tag__c,
Quantity__c,
Agreement_Line__c,
Products__c,
Site__c,
Customer__c from Installed_Products__c where Customer__c=:customer AND Products__c IN:proIds limit 4];

For(Installed_Products__c ip :iproducts ) 
{ 
iprodIds.add(ip.Id);
}
List<Products_Under_Service__c> Productserrvice =[select id,name,Installed_Productss__c from Products_Under_Service__c 
where Agreement_Line__c=:AgreementLineId AND Installed_Productss__c IN:iprodIds ];

For(Installed_Products__c ip :iproducts ) 
{
integer i=0;
For(integer temp=0;temp<Productserrvice .size();temp++ )
{
if(Productserrvice[temp].Installed_Productss__c == ip.id)
i++;
}
if(i==0)
ProductsUnderServiceList.add(new ProductsUnderService(ip));
} 
if(ProductsUnderServiceList.isEmpty())
ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,+ 'There are no Installed Products for '+customerName+' Account'));
return ProductsUnderServiceList; 
} 

public PageReference Add() 
{
List<Products_Under_Service__c> listPus; 
for(ProductsUnderService ip:ProductsUnderServiceList)
{
if(ip.selected==true)
{
Products_Under_Service__c pus= new Products_Under_Service__c(Installed_Productss__c=ip.id,
Agreement_Line__c =AgreementLineId);
//insert Pus; 
//listPus.add(pus);
}
insert listPus;
}
PageReference p=new PageReference('https://ap1.salesforce.com/'+AgreementLineId);
return p;
}
public PageReference cancel()
{
PageReference p=new PageReference('https://ap1.salesforce.com/'+AgreementLineId);
return p;
}

public class ProductsUnderService 
{
public Installed_Products__c con {get; set;}
public String id{get;set;}
public Boolean selected {get; set;}
public String aggreementLine{get;set;} 

public ProductsUnderService(Installed_Products__c ip)
{
id=ip.id;
con = ip;
selected = false;
}
}
}

Any help is Appriciated