Hi,

I got this error.

System.NullPointerException: Argument cannot be null.
Error is in expression '{!saveFile}' in page attachfile

My code:
//vf
<apex:page standardController="Bio_Briefing__c" extensions="upLoadExtension" showHeader="false" sidebar="false">

<apex:form >
<apex:pageMessages />
<apex:pageBlock title="Attach File" >

<h1>1.Select the File</h1>
<p>Type the path of the file or click the Browse button to find the file </p>
<apex:inputFile value="{!attachment.body}" filename="{!attachment.name}" fileSize="{!attachment.bodyLength}" contentType="{!attachment.contentType}" id="file"/>
<br/>




<h1>2.Click the "Attach File" button.</h1>
<p>Repeat steps 1 and 2 to attach multiple files </p>
<p>(When the upload is completed the file information will appear below)</p><br/>
<apex:commandButton value="Attach File" action="{!upload}"/>

<br/>
<h1>3.Click the Done button to return to the previous page</h1>
<p>(This will cancel an in-progress upload. )</p><br/>
<apex:commandButton value="Done" action="{!saveFile}"/>

</apex:pageBlock>
</apex:form>


</apex:page>

//controller

public class upLoadExtension{

private id bioId;
public blob photo;
public String image;
public Bio_Briefing__c bioBriefing{get;set;}
public uploadExtension(ApexPages.StandardController controller) {

this.bioId = ApexPages.currentPage().getParameters().get('id');
bioBriefing = new Bio_Briefing__c();
bioBriefing = [Select Id,Biographic_Photo__c from Bio_Briefing__c where id=:bioId];

}

public Attachment attachment {
get {
if (attachment == null)
attachment = new Attachment();
return attachment;
}
set;
}
public PageReference upload() {

attachment.OwnerId = UserInfo.getUserId();
attachment.ParentId = bioBriefing.Id; // the record the file is attached to
attachment.IsPrivate = true;

try {
insert attachment;
} catch (DMLException e) {
ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR,'Error uploading attachment'));
return null;
} finally {
attachment = new Attachment();
}

return null;

}
public PageReference saveFile(){

photo=attachment.body;
image=bioBriefing.Biographic_Photo__c;
if(image==null){
image=EncodingUtil.base64Encode(photo);
}
insert biobriefing;
PageReference ReturnPage = new PageReference('/'+ApexPages.currentPage().getParameters().get('id'));
ReturnPage.setRedirect(true);
return ReturnPage;
}
}