diff --git a/src/ApiDefinition.php b/src/ApiDefinition.php
index a9e3c8f..72dfbc8 100644
--- a/src/ApiDefinition.php
+++ b/src/ApiDefinition.php
@@ -810,7 +810,7 @@ private function getMethodsAsArray(array $resources)
 
     private function setProtocolsFromBaseUri(): void
     {
-        $schema = \mb_strtoupper(\parse_url($this->baseUri, PHP_URL_SCHEME));
+        $schema = \mb_strtoupper(\parse_url($this->baseUri, PHP_URL_SCHEME) ?? '');
 
         $this->protocols = empty($schema) ? [self::PROTOCOL_HTTPS, self::PROTOCOL_HTTP] : [$schema];
     }