Hi,

I'm developing apex class to send mass emails from selected records, when i select records and click on send button it show runtime error.

I'm getting this error message

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

Wat may be the problem? Please help me to rectify this.

Apex Class code:

public class wrapperClassController3 {
public String aMessage {
        get; set;   
    }
    public List<ID> studentids;
    public List<string> studentList1=new List<string>();
    //public String[] studentList1 = new List<String>();
    //Our collection of the class/wrapper objects cStudent 
    public List<cStudent> studentList {get; set;}
    
    //This method uses a simple SOQL query to return a List of Students
    public List<cStudent> getStudents(){
        if(studentList == null){
            studentList = new List<cStudent>();
        
            for(Student__c c : [select Id, First_Name__c,Last_Name__c, Email__c from Student__c limit 10]){
                
                studentList.add(new cStudent(c));
            }
        }
        return studentList;
    }
    
    public PageReference processSelected(){
        /*We create a new list of Student that we be populated only with Students
        if they are selected*/
        List<Student__c> selectedStudents = new List<Student__c>();
           this.aMessage = '';
        /*We will cycle through our list of cStudents and will check to see if the 
        selected property is set to true, if it is we add the Contact to the 
        selectedStudentss list. */
        for(cStudent cCon : getStudents()){
            if(cCon.selected == true){
                selectedStudents.add(cCon.con);
            }
        }
        
        /* Now we have our list of selected contacts and can perform any type of 
        logic we want, sending emails, updating a field on the Contact, etc */
        System.debug('These are the selected Students...');
        Integer numselectedStudents = selectedStudents.size();
        Integer counter = 0;
        System.Debug(selectedStudents);
        for(Student__c con : selectedStudents){
            counter++;
            //system.debug(con);
           
                if(counter==numselectedStudents) {
                    this.aMessage += con.Id + ','+ con.First_Name__c+',' + con.Email__c;
                    studentList1.add(con.Id);
                } else {
                    this.aMessage += con.Id + ','+con.First_Name__c+','+ con.Email__c+', ';
                }
            
        }
        return null;
        
        
       
    }
    
    /* This is our wrapper/container class. A container class is a class, a data 
    structure, or an abstract data type whose instances are collections of other 
    objects. In this example a wrapper class contains both the standard salesforce 
    object Contact and a Boolean value */
    public class cStudent
    {
       public Student__c con {get; set;}
        public Boolean selected {get; set;}
        
        /*This is the contructor method. When we create a new cContact object we pass a 
        Contact that is set to the con property. We also set the selected value to false*/
      public cStudent(Student__c c){
            con = c;
            selected = false;
            
        }
    }
    
   // public class mail
    //{
     //   public String subject { get; set; }
        
       // public String body{ get; set; }
        
        public PageReference send()
        {
            
            Messaging.MassEmailMessage email = new Messaging.MassEmailMessage();
//            String[] toAddresses = new String[] {};
            List<String> TargetObjectIds = new List<String>(); 
            //for(String s:studentList1)
            //{
             // String[] toAddresses = new String[] {s};
             //     TargetObjectIds.add(s);
            //}
//            ID s;
 
            for(ID s:studentids)
            {
               TargetObjectIds.add(s);
            }
            email.setSubject( 'subject' );
            
            //String[] toMassTargetObjects  = new String[]{toMassTargetObjects};
            email.setTargetObjectIds(TargetObjectIds);
            //email.setPlainTextBody( body );
            email.setReplyTo('chiranjeevi@datasisar.com');
            email.setSenderDisplayName('Customer Support');
            try{
                    Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.MassEmailMessage[] {email});   
                    PageReference Page = new PageReference('/mailinfo');
                    Page.setRedirect(true);
                    return Page;
                //  return null;
                }
           catch(Exception e)
           {
                return null;
           }
        
        
        
        
        } 
    
    //}
}

Visualforce Code.

<apex:page controller="wrapperClassController3">
<apex:outputPanel id="selected"><b>Selected: {!aMessage}</b></apex:outputPanel>
<apex:form >
<apex:pageBlock >
<apex:pageBlockButtons >
<apex:commandButton value="Process Selected" action="{!processSelected}" rerender="selected"/>
<apex:commandButton value="Send" action="{!send}"/>
</apex:pageBlockButtons>
<!-- In our table we are displaying the cStudent records -->
<apex:pageBlockTable value="{!students}" var="c" id="table">
<apex:column >
<!-- This is our selected Boolean property in our wrapper class -->
<apex:inputCheckbox value="{!c.selected}"/>
</apex:column>
<!-- This is how we access the student values within our cStudent container/wrapper -->
<apex:column value="{!c.con.First_Name__c}" />
<apex:column value="{!c.con.Last_Name__c}" />
<apex:column value="{!c.con.Email__c}" />
</apex:pageBlockTable>
</apex:pageBlock>
</apex:form>
</apex:page>

Thank you.