[SelectField] Not accepting null in array

[BlockChange]

When I return null within a SelectField instead of a MenuItem (with a .map on an array) I get the infamous There is an internal error in the React performance measurement code. Did not expect componentDidUpdate timer to start while render timer is still in progress for another instance. error, but after that:

DropDownMenu.js:250 Uncaught TypeError: Cannot read property 'props' of null

I have to return an empty div to fix this.

And when I try to put the MenuItems in an array, I get (only when I open the menu):

warning.js:44 Warning: flattenChildren(...): Encountered two children with the same key, `1:$.$0`. Child keys must be unique; when two children share a key, only the first child will be used.
    in div (created by List)
    in List (created by Menu)
    in div (created by Menu)
    in ClickAwayListener (created by Menu)
    in Menu (created by DropDownMenu)
    in div (created by Paper)
    in Paper (created by PopoverAnimationVertical)
    in PopoverAnimationVertical
    in MuiThemeProvider

Even though I've keyed the children.

When I return a div instead of nothing or null then I get:

Unknown props `desktop`, `focusState` on <div> tag. Remove these props from the element. For details, see https://fb.me/react-unknown-prop
    in div (created by Menu)
    in div (created by List)
    in List (created by Menu)
    in div (created by Menu)
    in ClickAwayListener (created by Menu)
    in Menu (created by DropDownMenu)
    in div (created by Paper)
    in Paper (created by PopoverAnimationVertical)
    in PopoverAnimationVertical
    in MuiThemeProvider