diff --git a/src/PipelineBuilder.php b/src/PipelineBuilder.php
index 217d191..cddc39c 100644
--- a/src/PipelineBuilder.php
+++ b/src/PipelineBuilder.php
@@ -26,7 +26,7 @@ public function add(callable $stage)
     /**
      * Build a new Pipeline object
      *
-     * @param  ProcessorInterface $processor
+     * @param  ProcessorInterface|null $processor
      *
      * @return Pipeline
      */