diff --git a/src/helpers/stringFunctions/stringFunctions.ts b/src/helpers/stringFunctions/stringFunctions.ts
index e29e709..7e0677b 100644
--- a/src/helpers/stringFunctions/stringFunctions.ts
+++ b/src/helpers/stringFunctions/stringFunctions.ts
@@ -8,9 +8,17 @@ import { randomUUID } from 'crypto';
 import { sha256 } from 'js-sha256';
 import uuidByString from 'uuid-by-string';
 
-export const startsWith = (str: string, startStr: string): boolean => str.startsWith(startStr);
+export const startsWith = (str: string | undefined, startStr: string): boolean | undefined => {
+  // undefined inputs always return undefined
+  if (typeof str === 'undefined') return undefined;
+  return str.startsWith(startStr);
+};
 
-export const endsWith = (str: string, endStr: string): boolean => str.endsWith(endStr);
+export const endsWith = (str: string | undefined, endStr: string): boolean | undefined => {
+  // undefined inputs always return undefined
+  if (typeof str === 'undefined') return undefined;
+  return str.endsWith(endStr);
+};
 
 export const initCapOnce = (str: string): string => {
   // used for polymorhic element names, where all type names need to