🐛 default to empty array in sumBy & countBy

Author: shashi278

src/lang.ts

@@ -236,7 +236,7 @@ export const sumBy = <T>(
   fn: (x: T) => number,
 ): number => {
   let s = 0;
-  for (const item of items) {
+  for (const item of items ?? []) {
     s += fn(item);
   }
   return s;
@@ -247,7 +247,7 @@ export const countBy = <T>(
   fn: (x: T) => boolean,
 ): number => {
   let s = 0;
-  for (const item of items) {
+  for (const item of items ?? []) {
     if (fn(item)) {
       s++;
     }