Warning after the upgrade to WP 4.4

Had the same problem on one of my sites. As James Huff pointed on WordPress 4.4 Master List a few hours ago, a patch for this problem has been made:

https://core.trac.wordpress.org/attachment/ticket/34723/34723.patch

To fix, open your category-template.php and replace lines 1144 – 1158…

function get_the_terms( $post, $taxonomy ) {
	if ( ! $post = get_post( $post ) )
		return false;
	$terms = get_object_term_cache( $post->ID, $taxonomy );
	if ( false === $terms ) {
		$terms = wp_get_object_terms( $post->ID, $taxonomy );
		$to_cache = array();
		foreach ( $terms as $key => $term ) {
			$to_cache[ $key ] = $term->data;
		}
		wp_cache_add( $post->ID, $to_cache, $taxonomy . '_relationships' );
	}
	$terms = array_map( 'get_term', $terms );

New code from the patch:

function get_the_terms( $post, $taxonomy ) {
	if ( ! $post = get_post( $post ) )
		return false;
	$terms = get_object_term_cache( $post->ID, $taxonomy );
 	if ( false === $terms ) {
 		$terms = wp_get_object_terms( $post->ID, $taxonomy );
		if ( ! is_wp_error( $terms ) ) {
			$to_cache = array();
			foreach ( $terms as $key => $term ) {
				$to_cache[ $key ] = $term->data;
			}
			wp_cache_add( $post->ID, $to_cache, $taxonomy . '_relationships' );
 		}
 	}
	if ( ! is_wp_error( $terms ) ) {
		$terms = array_map( 'get_term', $terms );
	}

So is now line 1144 – 1162. This fix will be included in the future 4.4.1 I suppose