Add typing for ArrayAccess

Author: gordalina

src/Console/Config.php

@@ -33,24 +33,26 @@ public function __construct(array $config = [])
         }
     }
 
-    public function offsetExists($offset)
+    public function offsetExists(mixed $offset): bool
     {
         return isset($this->config[$offset]);
     }
 
-    public function offsetGet($offset)
+    public function offsetGet(mixed $offset): mixed
     {
         if ($this->offsetExists($offset)) {
             return $this->config[$offset];
         }
+
+        return null;
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet(mixed $offset, mixed $value): void
     {
         $this->config[$offset] = $value;
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset(mixed $offset): void
     {
         unset($this->config[$offset]);
     }