fix(react-norhtstar): resolve TS errors exposed by TS 4.7

Author: Hotell

packages/fluentui/react-northstar/src/components/Portal/Portal.tsx

@@ -99,7 +99,7 @@ export const Portal: React.FC<PortalProps> & FluentComponentStaticProps<PortalPr
 
   const renderPortal = (): JSX.Element | undefined => {
     const contentToRender = childrenExist(children) ? children : content;
-    const focusTrapZoneProps = (_.keys(trapFocus).length && trapFocus) || {};
+    const focusTrapZoneProps = typeof trapFocus === 'boolean' ? {} : trapFocus;
     return (
       open && (
         <Ref innerRef={portalRef}>