diff --git a/articles/flow/create-ui/element-api/client-server-rpc.adoc b/articles/flow/create-ui/element-api/client-server-rpc.adoc
index 148cdfa72f..3704a516cc 100644
--- a/articles/flow/create-ui/element-api/client-server-rpc.adoc
+++ b/articles/flow/create-ui/element-api/client-server-rpc.adoc
@@ -107,6 +107,8 @@ You can use it anywhere in your client-side Polymer class implementation, and yo
 - enumeration type which is addressed via a string value from the client-side JavaScript; and
 - `TemplateModel` property types (see <</flow/create-ui/templates/polymer/model-bean#,Using Beans with a PolymerTemplate Model>>).
 
+A `null` argument is received as Java `null` (not [classname]`JsonNull`), or as the default value for primitive parameters.
+
 The client-side method returns a Promise, which is resolved asynchronously with the return value from the server, or `null` if the server-side return type is `void`. You can wait for the result using [methodname]`Promise.then()`. In an `async` function, the `await` keyword can also be used to wait for the result.
 
 This example uses [methodname]`this.$server.getGreeting()` to call a server-side method and `await` the result: