SortableTable::get_additional_url_paramstring() - http_build_query() throws fatal error

SortableTable::get_additional_url_paramstring()
The first http_build_query() throws fatal error when $this->additional_parameters is not an array

The error surfaced when viewing the index of an "Attendances" tool. (main/attendance/index.php)

main/inc/lib/sortable_table.class.php

@@ -975,7 +975,10 @@ class SortableTable extends HTML_Table
      */
     public function get_additional_url_paramstring()
     {
-        $result = http_build_query($this->additional_parameters);
+        $result = '';
+        if (is_array($this->additional_parameters)) {
+            $result = http_build_query($this->additional_parameters);
+        }
         foreach ($this->other_tables as $index => &$tablename) {
             $param = [];
             if (isset($_GET[$tablename.'_direction'])) {
@@ -996,7 +999,7 @@ class SortableTable extends HTML_Table
                 $param[$tablename.'_column'] = intval($_GET[$tablename.'_column']);
             }
             if (count($param) > 0) {
-                $result .= '&'.http_build_query($param);
+                $result .= (strlen($result) > 0 ? '&' : '').http_build_query($param);
             }
         }