Get All posts by tag in a network - wordpress multisite

code.php

<?php
/*
*
* Uses: get_tagged_post() or get_tagged_post( AN ARRAY OF BLOG IDs )
*
*/
function get_tagged_post($blogs = array(), $tag) {
	
	if( count( $blogs ) < 1 ){
		$blog_list = wp_get_sites(); 
		foreach ( $blog_list as $blog ) {
			array_push( $blogs, $blog['blog_id'] );
		}
	}
	$posts = array();
	
	foreach( $blogs as $blog ){
		switch_to_blog( $blog );
		$args = array(
			'tax_query' => array(
				array(
					'taxonomy' => 'post_tag',
					'field' => 'slug',
					'terms' => $tag
				)
			)
		);
		$tagged_posts = get_posts( $args );
		foreach( $tagged_posts as $tagged_post ){
			array_push( $posts, array(
						  'title' => $tagged_post->post_title,
						  'link' => get_permalink( $tagged_post->ID )
						  ) );
		}
		
		restore_current_blog();
	}
	
	?>
	<ul class="tagged_posts">
		<?php foreach( $posts as $post ) { ?>
		<li><a href="<?php echo $post['link'] ?>"><?php echo $post['title']; ?></a></li>
		<?php } ?>
	</ul>
	<?php
	
}


get_tagged_post( array(), 'popular' );