codeigniter验证应该仅在电子邮件ID数组不为空时才有效

I am doing codeigniter validation for email id. I have declared 3 text box for entering email id. I am retrieving all the 3 email id's in array called ref_email. now I want to do email id validation only when email id text boxes are not empty and show error message in view page. if email id text boxes are empty, then i don't want to do any validation. I don't know where i have done mistake in my code.I am doing codeigniter validation for email id.