fix: null check headshot

src/ts/app.ts

@@ -107,6 +107,7 @@ declare const Prism: any;
 
     let avatarType = 0;
     const headshot = document.getElementById("index-headshot") as HTMLImageElement;
+    if (headshot) {
         headshot.addEventListener("click", (ev: MouseEvent) => {
             if (avatarType === 0) {
                 headshot.classList.add("headshot-spin", "headshot-spin-start");
@@ -134,4 +135,5 @@ declare const Prism: any;
                 }, 400);
             }
         });
+    }
 })();