[SalesForce] REQUIRED_FIELD_MISSING, No body specified in the file attachment:

I have a requirement whenever I create a record and upload a word file document in notes and attachment a trigger gets fired which send that attachment to a desired email address.

I have written this trigger which sends email when a record is created but when I try to add attachment code it shows this error.
REQUIRED_FIELD_MISSING, No body specified in the file attachment:
But when I check in debug I get the Body as Blob[0].

trigger SendMail on Random__c (after update) 
{

Set<ID> RandomIDs = new Set<ID>();
for(Random__c c : trigger.new)
{
    RandomIDs.add(c.id);

}
  List<Attachment> lstAttach = [SELECT id, Name, body, ContentType FROM Attachment WHERE ParentId IN : RandomIDs];
 for(Candidate__c c : trigger.new)
{

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

    for(Attachment att : lstAttach)
    {
         // Create the email attachment

         Messaging.EmailFileAttachment efa = new Messaging.EmailFileAttachment();       
         efa.setFileName(att.Name);
         efa.Body = att.body;
         efa.setContentType('application/msWord');
         efa.setInline(false);
     email.setFileAttachments(new Messaging.EmailFileAttachment[] {efa});

    }



    String subject = 'Sample subject ';
    email.setSubject(subject);

    String body = ' Sample Body '; 
    email.setPlainTextBody(body);

    email.setToAddresses(new String[]{'test@test.com'});

    if(email != null)
      {

        Messaging.sendEmail(new Messaging.singleEmailMessage[] {email});

      }
  }
}