fix(curriculum): add optional chaining (freeCodeCamp#59534)

Author: clarencepenz

Diff for: curriculum/challenges/english/25-front-end-development/workshop-storytelling-app/671fafbae959c048d82bac8d.md

@@ -23,7 +23,7 @@ function rgbToHex(rgb) {
   return (
     "#" +
     rgbValues
-      .map((num) => parseInt(num).toString(16).padStart(2, "0"))
+      ?.map((num) => parseInt(num).toString(16).padStart(2, "0"))
       .join("")
   );
 }
@@ -46,7 +46,7 @@ function rgbToHex(rgb) {
   return (
     "#" +
     rgbValues
-      .map((num) => parseInt(num).toString(16).padStart(2, "0"))
+      ?.map((num) => parseInt(num).toString(16).padStart(2, "0"))
       .join("")
   );
 }
@@ -69,7 +69,7 @@ function rgbToHex(rgb) {
   return (
     "#" +
     rgbValues
-      .map((num) => parseInt(num).toString(16).padStart(2, "0"))
+      ?.map((num) => parseInt(num).toString(16).padStart(2, "0"))
       .join("")
   );
 }