Check that author variable is of the expected type

changelog/fix-variable-type-mismatch

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Check that author variable is of the expected type

includes/class-sensei-modules.php

@@ -2334,8 +2334,8 @@ public static function get_term_authors( $term_name ) {
 	 *
 	 * @since 1.8.0
 	 *
-	 * @param $slug
-	 * @return WP_User $author if no author is found or invalid term is passed the admin user will be returned.
+	 * @param string $slug The term slug to get the author for.
+	 * @return WP_User|false WP_User if found, false if no valid author found.
 	 */
 	public static function get_term_author( $slug = '' ) {
 
@@ -2721,13 +2721,12 @@ public function append_teacher_name_to_module( $terms, $taxonomies, $args ) {
 
 			$author = self::get_term_author( $term->slug );
 
-			if ( ! user_can( $author, 'manage_options' ) && isset( $term->name ) ) {
+			if ( ! user_can( $author, 'manage_options' ) && isset( $term->name ) && $author instanceof WP_User ) {
 				$term->name = $term->name . ' (' . $author->display_name . ') ';
 			}
 
 			// add the term to the teachers terms
 			$users_terms[] = $term;
-
 		}
 
 		return $users_terms;