Check value isset to avoid PHP notice

src/Symfony/Component/Console/Style/SymfonyStyle.php

@@ -290,7 +290,7 @@ public function choice(string $question, array $choices, $default = null)
     {
         if (null !== $default) {
             $values = array_flip($choices);
-            $default = $values[$default];
+            $default = isset($values[$default]) ? $values[$default] : $default;
         }
 
         return $this->askQuestion(new ChoiceQuestion($question, $choices, $default));