PHP

check if $_files is empty php

if($_FILES['cover_image']['size'] == 0) {
// No file was selected for upload, your (re)action goes here
}

check if file empty php

  if(filesize("path/to/file") == 0){
    print "File is empty";
  }

CHECKING IF FILE IS EMPTY IN PHP

## CHECKS IF FILE IS EMPTY
if ($_FILES['file']['size'] == 0 && $_FILES['file']['error'] == 0)
{
    // file is empty (and not an error)
}