fix: prevent parser throwing when err is null (#41278)

tools/challenge-parser/parser/index.js

@@ -55,10 +55,10 @@ exports.parseMD = function parseMD(filename) {
       if (!err) {
         delete file.contents;
         resolve(file.data);
-      }
-
+      } else {
         err.message += ' in file ' + filename;
         reject(err);
+      }
     });
   });
 };