I have a trigger which makes a callout to a controller which is using @future annotation. The controller then call a email class to send out the email with the pdf attachment. But I get the following error in the debug logs:

Status java.lang.NullPointerException Application Browser
Request Type Api Operation FutureHandler
Duration (ms) 528 Log Length 887
Log

20090225222643.115:Class.myOpportunityController.createSamplevfpdf: line 8, column 5: controller method called
20090225222643.115:Class.myOpportunityController.createSamplevfpdf: line 10, column 5: vf opp id: 0068000000M1lOCAAZ
20090225222643.115:Class.myOpportunityController.createSamplevfpdf: line 11, column 5: vf opp name: United Oil Installations
20090225222643.115:Class.myOpportunityController.createSamplevfpdf: line 12, column 5: vf con id: 0038000000UJtnFAAT
20090225222643.115:Class.myOpportunityController.createSamplevfpdf: line 13, column 5: vf con name: Stella Pavlova
20090225222643.115:Class.myOpportunityController.createSamplevfpdf: line 14, column 5: vf con email: spavlova@uog.com
System.VisualforceException: java.lang.NullPointerException

Class.sendPDFEmailClass.sendmyEmail: line 8, column 20
Class.myOpportunityController.createSamplevfpdf: line 16, column 5

Trigger:

trigger OpportunityVFEmail on Opportunity (after insert, after update)
{

for(Opportunity a: Trigger.new){

System.debug('id is: ' + a.Id);

System.debug('name is : ' + a.Name);

System.debug('same custom field: ' + a.same__c);

if (a.stageName == 'Closed Won')
{
Contact con1 = [select id, name, email, accountid from Contact
where accountid = :a.accountid limit 1];

System.debug('contact id: ' + con1.id);
System.debug('contact name: ' + con1.name);
System.debug('contact email: ' + con1.email);
String con_id = con1.id;
String con_name = con1.name;
String con_email = con1.email;
System.debug('s contact id: ' + con_id);
System.debug('s contact name: ' + con_name);
System.debug('s contact email: ' + con_email);

String opp_id = a.id;
String opp_name = a.name;
System.debug('S opp name: ' + opp_id);
System.debug('S opp name: ' + opp_name);

myOpportunityController.createSamplevfpdf(a.id, a.name, con1.id, con1.name, con1.email);
}
}
}

Controller:

global class myOpportunityController {

@future (callout=true)
public static void createSamplevfpdf(ID id, String Opp_name, String Con_id, String Con_name, String Con_email)
{
Opportunity opp;
Contact con1;
System.debug('controller method called');

System.debug('vf opp id: ' + id);
System.debug('vf opp name: ' + Opp_name);
System.debug('vf con id: ' + Con_id);
System.debug('vf con name: ' + Con_name);
System.debug('vf con email: ' + Con_email);

sendPDFEmailClass.sendmyEmail(id,Opp_name, Con_id, Con_name, Con_email);
}

}

 Email Apex Class:

global class sendPDFEmailClass
{
public static void sendmyEmail(ID EOpp_id, String EOpp_name, String ECon_id, String ECon_name, String ECon_email)
{

PageReference samplevfpdf = Page.samplevfpdf;
samplevfpdf.getParameters().put('id',EOpp_id);
Blob pdf1 = samplevfpdf.getContent();


Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();

String[] toAddresses = new String[] {ECon_email}; //get it from contacts
mail.setToAddresses(toAddresses);
mail.setReplyTo('user@salesforce.com');//sf user email add
mail.setSenderDisplayName('xxxxxxxxxx');//sf user name

mail.setSubject(' New Account Purchase Details' + 'Invoice no' + ': ' + ECon_name + ' ' + EOpp_name + ' : ' + EOpp_id);

mail.setBccSender(true);
mail.setUseSignature(true);

mail.setPlainTextBody('This is a test email');
mail.setHtmlBody('Welcome to ');

//Attachments

Messaging.EmailFileAttachment mailAttachment;
mailAttachment = new Messaging.EmailFileAttachment();
mailAttachment.setFileName('samplevfattachment.pdf');
mailAttachment.setBody(pdf1);
mail.setFileAttachments(new Messaging.EmailFileAttachment[] { mailAttachment });

//mail.setFileAttachments(fileAttachments);

//send the email
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });

}

}

 I'm not sure why I get this error? Is it related to the use of @future? Can anyone let me know how I should resolve it?

Thanks