doc: note that randomBytes throws when passed null

Fixes: nodejs#16778

PR-URL: nodejs#17594
Fixes: nodejs#16778
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>

doc/api/crypto.md

@@ -1792,6 +1792,11 @@ be passed instead of a public key.
 ### crypto.randomBytes(size[, callback])
 <!-- YAML
 added: v0.5.8
+changes:
+  - version: v9.0.0
+    pr-url: https://github.com/nodejs/node/pull/16454
+    description: Passing `null` as the `callback` argument now throws
+                 `ERR_INVALID_CALLBACK`.
 -->
 - `size` {number}
 - `callback` {Function}