diff --git a/src/__tests__/utils.test.ts b/src/__tests__/utils.test.ts
new file mode 100644
index 0000000..8a26745
--- /dev/null
+++ b/src/__tests__/utils.test.ts
@@ -0,0 +1,15 @@
+import {nullishToOptional} from '../utils';
+
+describe('nullishToOptional', () => {
+  it('should return undefined for nullish values', () => {
+    expect(nullishToOptional(null)).toBeUndefined();
+    expect(nullishToOptional(undefined)).toBeUndefined();
+  });
+
+  it('should return the original value for non-nullish values', () => {
+    expect(nullishToOptional(0)).toBe(0);
+    expect(nullishToOptional('')).toBe('');
+    expect(nullishToOptional(false)).toBe(false);
+    expect(nullishToOptional('test')).toBe('test');
+  });
+});
diff --git a/src/offers/ticket-offer.ts b/src/offers/ticket-offer.ts
index a4d84f2..718f566 100644
--- a/src/offers/ticket-offer.ts
+++ b/src/offers/ticket-offer.ts
@@ -1,11 +1,12 @@
 import {z} from 'zod';
+import {nullishToOptional} from '../utils';
 
 /**
  * FlexDiscountStep in
  * https://github.com/AtB-AS/sales/blob/main/sales-service/src/flexible.rs
  */
 export const FlexDiscountStep = z.object({
-  expires: z.string().nullish(),
+  expires: z.string().nullish().transform(nullishToOptional),
   discount: z.number(),
 });
 export type FlexDiscountStep = z.infer<typeof FlexDiscountStep>;
@@ -26,11 +27,11 @@ export type FlexDiscountLadder = z.infer<typeof FlexDiscountLadder>;
  */
 export const SearchOfferPrice = z.object({
   originalAmount: z.string(),
-  originalAmountFloat: z.number().nullish(),
+  originalAmountFloat: z.number().nullish().transform(nullishToOptional),
   amount: z.string(),
-  amountFloat: z.number().nullish(),
+  amountFloat: z.number().nullish().transform(nullishToOptional),
   currency: z.string(),
-  vatGroup: z.string().nullish(),
+  vatGroup: z.string().nullish().transform(nullishToOptional),
 });
 export type SearchOfferPrice = z.infer<typeof SearchOfferPrice>;
 
@@ -50,8 +51,8 @@ export enum OfferValidity {
  */
 export const TicketRoute = z.object({
   type: z.nativeEnum(OfferValidity),
-  from: z.string().nullish(),
-  to: z.string().nullish(),
+  from: z.string().nullish().transform(nullishToOptional),
+  to: z.string().nullish().transform(nullishToOptional),
 });
 export type TicketRoute = z.infer<typeof TicketRoute>;
 
@@ -64,12 +65,12 @@ export const TicketOffer = z.object({
   travellerId: z.string(),
   price: SearchOfferPrice,
   fareProduct: z.string(),
-  validFrom: z.string().nullish(),
-  validTo: z.string().nullish(),
-  flexDiscountLadder: FlexDiscountLadder.nullish(),
+  validFrom: z.string().nullish().transform(nullishToOptional),
+  validTo: z.string().nullish().transform(nullishToOptional),
+  flexDiscountLadder: FlexDiscountLadder.nullish().transform(nullishToOptional),
   route: TicketRoute,
   shouldStartNow: z.boolean(),
-  available: z.number().nullish(),
+  available: z.number().nullish().transform(nullishToOptional),
 });
 export type TicketOffer = z.infer<typeof TicketOffer>;
 
diff --git a/src/utils.ts b/src/utils.ts
new file mode 100644
index 0000000..19b419a
--- /dev/null
+++ b/src/utils.ts
@@ -0,0 +1,15 @@
+/**
+ * For use in cases where you want a value to be "optional" / `T | undefined`,
+ * but have to accept `null`.
+ *
+ * @example
+ * ```ts
+ * const Foo =  z.string().nullish().transform(nullishToOptional)
+ * type Foo = z.infer<typeof Foo>; // `type Foo = string | undefined`
+ * ```
+ */
+export function nullishToOptional<T>(
+  value: T | null | undefined,
+): T | undefined {
+  return value ?? undefined;
+}