Using conditional for empty fields

Hello guys, i need some help here,

I’m working on a filter/search, the problem is:

I want to use the radio buttons, so when click on it, will identify and request all posts with the custom field “filled in”, if this custom field is empty, will not return the post, anyone know how to do this?

Thanks!

http://ww.wp.xz.cn/extend/plugins/wp-custom-fields-search/