Remove empty p tags from WordPress posts by ninnypants https://gist.github.com/ninnypants/1668216
<?php
// don´t add the opening php tag in your functions! Paste from here
add_filter( 'the_content', 'remove_empty_p', 20, 1 );
function remove_empty_p( $content ){
// clean up p tags around block elements
$content = preg_replace( array(
'#<p>\s*<(div|aside|section|article|header|footer)#',
'#</(div|aside|section|article|header|footer)>\s*</p>#',
'#</(div|aside|section|article|header|footer)>\s*<br ?/?>#',
'#<(div|aside|section|article|header|footer)(.*?)>\s*</p>#',
'#<p>\s*</(div|aside|section|article|header|footer)#',
), array(
'<$1',
'</$1>',
'</$1>',
'<$1$2>',
'</$1',
), $content );
return preg_replace('#<p>(\s| )*+(<br\s*/*>)*(\s| )*</p>#i', '', $content);
}