[BUGFIX] new eslint rules fixed

Author: Gonzalo Diaz

src/projecteuler/helpers/product.ts

@@ -1,5 +1,5 @@
 export const product = (numList: number[] = []): number => {
-  if (!numList || numList.length === 0) return 0;
+  if (numList?.length === 0) return 0;
   return numList.reduce((previous, current) => previous * current, 1);
 };
 

src/projecteuler/helpers/sum.ts

@@ -1,5 +1,5 @@
 export const sum = (numList: number[] = []): number => {
-  if (!numList || numList.length === 0) return 0;
+  if (numList?.length === 0) return 0;
   return numList.reduce((previous, current) => previous + current, 0);
 };