MDL-33681 course: cannot have a section called '0'.

No reason to prevent this. It is just a matter of doing a proper test,
rather than the sloppy PHP !empty().

course/format/topics/lib.php

@@ -59,7 +59,7 @@ function callback_topics_definition() {
 
 function callback_topics_get_section_name($course, $section) {
     // We can't add a node without any text
-    if (!empty($section->name)) {
+    if ((string)$section->name !== '') {
         return format_string($section->name, true, array('context' => get_context_instance(CONTEXT_COURSE, $course->id)));
     } else if ($section->section == 0) {
         return get_string('section0name', 'format_topics');

course/format/weeks/lib.php

@@ -66,7 +66,7 @@ function callback_weeks_definition() {
  */
 function callback_weeks_get_section_name($course, $section) {
     // We can't add a node without text
-    if (!empty($section->name)) {
+    if ((string)$section->name !== '') {
         // Return the name the user set.
         return format_string($section->name, true, array('context' => context_course::instance($course->id)));
     } else if ($section->section == 0) {