Some code cleaning.

src/LinkGenerators/EntityLinkGenerator.php

@@ -25,22 +25,26 @@ abstract class EntityLinkGenerator {
       }
       $links = $this->get_entity_bundle_links($entity_type, $bundle, $language);
       $lastmod = NULL;
-      foreach ($links as $id => &$link) {
-        switch ($entity_type) {
-          case 'node':
-            $lastmod = db_query("SELECT changed FROM {node_field_data} WHERE nid = :nid LIMIT 1", array(':nid' => $id))->fetchCol();
-            break;
-          case 'taxonomy_term':
-            $lastmod = db_query("SELECT changed FROM {taxonomy_term_field_data} WHERE tid = :tid LIMIT 1", array(':tid' => $id))->fetchCol();
-            break;
-          case 'menu':
-            //todo: to be implemented
-        }
-        $this->entity_links[] = SitemapGenerator::add_xml_link_markup($link, $bundle_settings['priority'], isset($lastmod[0]) ? date_iso8601($lastmod[0]) : NULL);
+      foreach ($links as $id => $link) {
+        $this->entity_links[] = SitemapGenerator::add_xml_link_markup($link, $bundle_settings['priority'], $this->get_lastmod($entity_type, $id));
       }
     }
     return $this->entity_links;
   }
 
+  private function get_lastmod($entity_type, $id) {
+    switch ($entity_type) {
+      case 'node':
+        $lastmod = db_query("SELECT changed FROM {node_field_data} WHERE nid = :nid LIMIT 1", array(':nid' => $id))->fetchCol();
+        break;
+      case 'taxonomy_term':
+        $lastmod = db_query("SELECT changed FROM {taxonomy_term_field_data} WHERE tid = :tid LIMIT 1", array(':tid' => $id))->fetchCol();
+        break;
+      case 'menu':
+        //todo: to be implemented
+    }
+    return isset($lastmod[0]) ? date_iso8601($lastmod[0]) : NULL;
+  }
+
   abstract function get_entity_bundle_links($entity_type, $bundle, $language);
 }

src/LinkGenerators/EntityTypeLinkGenerators/taxonomy_term.php

@@ -20,7 +20,6 @@ class taxonomy_term extends EntityLinkGenerator {
 
   function get_entity_bundle_links($entity_type, $bundle, $language) {
 
-    //todo: check what happens if none existent.
     $results = db_query("SELECT tid FROM {taxonomy_term_field_data} WHERE vid = :vid", array(':vid' => $bundle))
       ->fetchAllAssoc('tid');