- Small fixes made to session

src/Session.php

@@ -8,17 +8,22 @@ use session_name, session_id, session_start, session_destroy, session_save_path,
 
 class Session
 {
-    public static function get($key, $default = null)
+    public static function get($key, $default = null) : mixed
     {
         return static::has($key) ? $_SESSION[$key] : $default;
     }
 
-    public static function set($key, $value)
+    public static function define($key, $value) : bool
+    {
+        return static::has($key) ? false : static::set($key, $value) || true;
+    }
+
+    public static function set($key, $value) : mixed
     {
         return $_SESSION[$key] = $value;
     }
 
-    public static function delete($key)
+    public static function delete($key) : void
     {
         unset($_SESSION[$key]);
     }