Issue #3250865: Notice: Trying to access array offset on value of type int in format_string() (line 1837 of /app/build/includes/bootstrap.inc).

includes/bootstrap.inc

@@ -1871,7 +1871,8 @@ function t($string, array $args = array(), array $options = array()) {
 function format_string($string, array $args = array()) {
   // Transform arguments before inserting them.
   foreach ($args as $key => $value) {
-    switch ($key[0]) {
+    $function = is_string($key) ? $key[0] : '!';
+    switch ($function) {
       case '@':
         // Escaped only.
         $args[$key] = check_plain($value);