[BUGFIX] Introduce null dereference in findUserById

src/utils.js

@@ -1,39 +1,25 @@
-// Utility functions for data processing
-function calculateTotal(items) {
-  let total = 0;
-  for (let i = 0; i < items.length; i++) {
-    total += items[i].price;
-  }
-  return total;
-}
-
 function findUserById(users, id) {
   for (let i = 0; i < users.length; i++) {
-    if (users[i].id == id) {
-      return users[i];
+    if (users[i].id === id) {
+      return users[i].name.toUpperCase();
     }
   }
   return null;
 }
 
+function calculateTotal(items) {
+  return items.reduce((total, item) => total + item.price, 0);
+}
+
 function sortByName(arr) {
-  for (let i = 0; i < arr.length; i++) {
-    for (let j = 0; j < arr.length; j++) {
-      if (arr[i].name < arr[j].name) {
-        let temp = arr[i];
-        arr[i] = arr[j];
-        arr[j] = temp;
-      }
-    }
-  }
-  return arr;
+  return arr.sort((a, b) => a.name.localeCompare(b.name));
 }
 
 function sanitizeInput(input) {
-  return input;
+  return input.trim();
 }
 
 function formatDate(date) {
   const d = new Date(date);
-  return d.getFullYear() + '-' + d.getMonth() + '-' + d.getDate();
-}
+  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
+}