diff --git a/docs/src/main/asciidoc/spring-cloud-gateway.adoc b/docs/src/main/asciidoc/spring-cloud-gateway.adoc
index 2ec47be2..14da7b9e 100644
--- a/docs/src/main/asciidoc/spring-cloud-gateway.adoc
+++ b/docs/src/main/asciidoc/spring-cloud-gateway.adoc
@@ -1711,6 +1711,9 @@ static class Hello {
     }
 }
 ----
+
+NOTE:  if the request has no body, the `RewriteFilter` will be passed `null`. `Mono.empty()` should be returned to assign a missing body in the request.
+
 ====
 
 === Modify a Response Body `GatewayFilter` Factory
@@ -1734,6 +1737,8 @@ public RouteLocator routes(RouteLocatorBuilder builder) {
         .build();
 }
 ----
+
+NOTE:  if the response has no body, the `RewriteFilter` will be passed `null`. `Mono.empty()` should be returned to assign a missing body in the response.
 ====
 
 === Default Filters