diff --git a/Extractor/ApiDocExtractor.php b/Extractor/ApiDocExtractor.php
index 133a2d5..445b3ed 100644
--- a/Extractor/ApiDocExtractor.php
+++ b/Extractor/ApiDocExtractor.php
@@ -390,6 +390,9 @@ class ApiDocExtractor
      *  - Array parameters are recursively merged.
      *  - Non-null default values prevail over null default values. Later values overrides previous defaults.
      *
+     * However, if newly-returned parameter array contains a parameter with NULL, the parameter is removed from the merged results.
+     * If the parameter is not present in the newly-returned array, then it is left as-is.
+     *
      * @param  array $p1 The pre-existing parameters array.
      * @param  array $p2 The newly-returned parameters array.
      * @return array The resulting, merged array.
@@ -399,9 +402,15 @@ class ApiDocExtractor
         $params = $p1;
 
         foreach ($p2 as $propname => $propvalue) {
+
+            if ($propvalue === null) {
+                unset($params[$propname]);
+                continue;
+            }
+
             if (!isset($p1[$propname])) {
                 $params[$propname] = $propvalue;
-            } else {
+            } elseif (is_array($propvalue)) {
                 $v1 = $p1[$propname];
 
                 foreach ($propvalue as $name => $value) {
diff --git a/Resources/config/services.xml b/Resources/config/services.xml
index da00c21..dbd694b 100644
--- a/Resources/config/services.xml
+++ b/Resources/config/services.xml
@@ -13,6 +13,8 @@
         <parameter key="nelmio_api_doc.extractor.handler.jms_security.class">Nelmio\ApiDocBundle\Extractor\Handler\JmsSecurityExtraHandler</parameter>
         <parameter key="nelmio_api_doc.extractor.handler.sensio_framework_extra.class">Nelmio\ApiDocBundle\Extractor\Handler\SensioFrameworkExtraHandler</parameter>
         <parameter key="nelmio_api_doc.extractor.handler.phpdoc.class">Nelmio\ApiDocBundle\Extractor\Handler\PhpDocHandler</parameter>
+
+        <parameter key="nelmio_api_doc.parser.collection_parser.class">Nelmio\ApiDocBundle\Parser\CollectionParser</parameter>
     </parameters>
 
     <services>
@@ -52,6 +54,10 @@
             <argument type="service" id="nelmio_api_doc.doc_comment_extractor" />
             <tag name="nelmio_api_doc.extractor.handler"/>
         </service>
+
+        <service id="nelmio_api_doc.parser.collection_parser" class="%nelmio_api_doc.parser.collection_parser.class%">
+            <tag name="nelmio_api_doc.extractor.parser" />
+        </service>
     </services>
 
 </container>