Dropdown onSelectedChanged typings incorrect

[berickson1]

Bug Report

The typescript typings for Drpodown onSelectedChanged specifies that it should be a ComponentEventHandler - in which event is always defined and may be defined
export declare type ComponentEventHandler<TProps> = (event: React.SyntheticEvent<HTMLElement>, data?: TProps) => void;
In this case TProps is DropdownProps

Steps

Create a Dropdown Component, select an item and observe parameters to onSelectedChanged callback

Expected Result

event object is defined (or typings reflect that it can be undefined/null)

Actual Result

event is null

Version

0.43.1

Testcase

https://codesandbox.io/s/fluent-ui-example-v9pf1