I get an error when the second parameter passed to imagejpeg is NULL.

Unable to open '' for writing in ...

I worked around the issue by changing the switch statement at the bottom:

{

Writing image according to type to the output destination

switch ( $info[2] ) {
case IMAGETYPE_GIF: ($output == NULL) ? imagegif($image_resized) : imagegif($image_resized, $output); break;
case IMAGETYPE_JPEG: ($output == NULL) ? imagejpeg($image_resized) : imagejpeg($image_resized, $output); break;
case IMAGETYPE_PNG: ($output == NULL) ? imagepng($image_resized) : imagepng($image_resized, $output); break;
default: return false;
}
}