Update src/BigBlueButton.php

Co-authored-by: Felix Jacobi <felix@jacobi-hamburg.net>

src/BigBlueButton.php

@@ -120,7 +120,7 @@ public function __construct(?string $baseUrl = null, ?string $secret = null, ?Tr
             @trigger_error(sprintf('Constructing "%s" without passing a server base URL is deprecated and will throw an exception 6.0.', self::class), \E_USER_DEPRECATED);
         }
 
-        if (empty($secret)) {
+        if (null === $secret) {
             @trigger_error(sprintf('Constructing "%s" without passing a secret is deprecated and will throw an exception 6.0.', self::class), \E_USER_DEPRECATED);
         }