diff --git a/src/AwsS3Adapter.php b/src/AwsS3Adapter.php
index e58c161..c015b27 100644
--- a/src/AwsS3Adapter.php
+++ b/src/AwsS3Adapter.php
@@ -217,7 +217,7 @@ public function deleteDir($dirname)
      */
     public function createDir($dirname, Config $config)
     {
-        return $this->upload($dirname . '/', '', $config);
+        return $this->upload($dirname . '/', null, $config);
     }
 
     /**
@@ -580,7 +580,7 @@ protected function upload($path, $body, Config $config)
         $options = $this->getOptionsFromConfig($config);
         $acl = array_key_exists('ACL', $options) ? $options['ACL'] : 'private';
 
-        if ( ! isset($options['ContentType'])) {
+        if ( ! is_null($body) && ! isset($options['ContentType'])) {
             $options['ContentType'] = Util::guessMimeType($path, $body);
         }