WordPress Login exception

Hello,
I am currently developing a wordpress driven buddypress site. I have a wordpress login placed on sidebar widget area. If the field is left empty and clicked on login button, I would be taken to wp-login.php. I would like to know if there is any function handle this exception. I am not well verse with php programming. I would like to apologise if this is a repost. Even If you provide the link to solution it would be highly appreciated. Thanks in advance.
Regards
Satish