Custom Menu Example (on the docs) wont work in v 3.0.0

[Abenezer]

Expected
Custom menu example to work
What happened instead:
Error: Expected ref to be a function, a string, an object returned by React.createRef(), or null.

Steps to reproduce:
Just Copy the custom menu example

I am guessing something to do with forwardRef and react router
Environment

• React-admin version: 3.0.0
• React version: 16.12
• Browser: chrome
• Stack trace (in case of a JS error):
  react-dom.development.js:14792 Uncaught Error: Expected ref to be a function, a string, an object returned by React.createRef(), or null.

[Abenezer]

ok after hours of searching (and looking at the source of the original Menu.js) i found the problem to be the left Icon property
it seems it only accepts materialized components
leftIcon={LabelIcon} wont work
leftIcon={<LabelIcon/>} works

if this is the official solution update the docs and close this issue