remove-empty-p.php

<?php
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|&nbsp;)*+(<br\s*/*>)*(\s|&nbsp;)*</p>#i', '', $content);
}