fix lint issues

Author: vas3a

src-ts/lib/portal/Portal.tsx

@@ -10,9 +10,9 @@ interface PortalProps {
 }
 
 const Portal: FC<PortalProps> = (props: PortalProps) => {
-    const portalNode: HTMLElement | null = props.portalId
+    const portalNode: HTMLElement | null | undefined = props.portalId
         ? document.getElementById(props.portalId)
-        :  props.portalNode ?? null
+        :  props.portalNode ?? undefined
 
     const defaultPortalNode: HTMLElement = useMemo(() => {
         if (props.portalId || props.portalNode) {