fix: handle empty string

src/app/pipes/upperfirst-pipe.ts

@@ -5,8 +5,8 @@ import { Pipe, PipeTransform } from '@angular/core';
 })
 export class UpperfirstPipe implements PipeTransform {
 
-  transform(value: string,) {
-    const upperFirst = value[0].toUpperCase();
+  transform(value: string) {
+    const upperFirst = value.charAt(0).toUpperCase();
     value = value.slice(1);
     return upperFirst + value;
   }