diff --git a/gateleen-core/src/main/java/org/swisspush/gateleen/core/storage/ResourceStorage.java b/gateleen-core/src/main/java/org/swisspush/gateleen/core/storage/ResourceStorage.java
index e4e51bfca..8af8cd07e 100644
--- a/gateleen-core/src/main/java/org/swisspush/gateleen/core/storage/ResourceStorage.java
+++ b/gateleen-core/src/main/java/org/swisspush/gateleen/core/storage/ResourceStorage.java
@@ -10,6 +10,15 @@
 public interface ResourceStorage {
     void get(String path, Handler<Buffer> bodyHandler);
 
+    /**
+     * <p>Under normal operation 'doneHandler' is called with the result. BUT: There are some impl
+     * which sometimes call it with 'null' as its value. It looks like this indicates that there was
+     * some kind of error. Most of the time impl knows exactly what the error was. But there is no
+     * way that it would report it to the caller (because this API does not provide a way to do so).</p>
+     *
+     * <p>There is yet another special case: Some impls in some cases do NOT call 'doneHandler' at
+     * all. So there is no way to know what happened behind the scene.</p>
+     */
     void put(String uri, MultiMap headers, Buffer buffer, Handler<Integer> doneHandler);
 
     void put(String uri, Buffer buffer, Handler<Integer> doneHandler);