diff --git a/src/Printer/CollectorMetadataPrinter.php b/src/Printer/CollectorMetadataPrinter.php
index a0ed8f61..b84a51b2 100644
--- a/src/Printer/CollectorMetadataPrinter.php
+++ b/src/Printer/CollectorMetadataPrinter.php
@@ -88,7 +88,7 @@ public function printArgTypesAsString(
         return implode('|', $stringArgTypes);
     }
 
-    public function printParamTypesToString(ClassMethod $classMethod, ?string $className): string
+    public function printParamTypesToString(ClassMethod $classMethod, string $className): string
     {
         $printedParamTypes = [];
         foreach ($classMethod->params as $param) {