Type corrections

I have a language server now.

thallium-frontend/src/utils/hooks.ts

@@ -1,4 +1,5 @@
-import { useMemo, useState, useEffect } from "react";
+import { useState, useEffect } from "react";
+import { type RefObject } from "react";
 
 export function useVisible(ref: RefObject<HTMLElement>) {
   const [isVisible, setVisible] = useState(false)
@@ -7,7 +8,8 @@ export function useVisible(ref: RefObject<HTMLElement>) {
     const observer = new IntersectionObserver(
         ([entry]) => setVisible(entry.isIntersecting)
     )
-    observer.observe(ref.current)
+    if (ref.current)
+      observer.observe(ref.current)
     return () => observer.disconnect()
   }, [])