describe("getSession", () => {
   const clientId = "testClient";
 
   it("should return empty string if no session is found", () => {
     const headers: HeadersLike = {};
     expect(getSession({ headers, clientId })).toBe("");
   });
 
+  it("should handle undefined headers", () => {
+    expect(getSession({ headers: undefined, clientId })).toBe("");
+  });
+
+  it("should handle null headers", () => {
+    expect(getSession({ headers: null, clientId })).toBe("");
+  });
+

 const getFromCookie = (headers: HeadersLike, clientId: string) => {
   const cookie = headers?.cookie;
-  if (typeof cookie !== "string") {
-    return;
-  }
+  if (typeof cookie !== "string") return null;
   const re = new RegExp(`auth.${clientId}.session=(.+?)(?:;|$)`);
-  const match = cookie.match(re);
-  if (!match) {
-    return;
-  }
-  return match[1];
+  return cookie.match(re)?.[1] ?? null;
 };
 

-export const getSession = ({ headers, clientId }: GetSessionProps): string => {
+export const getSession = ({ headers, clientId }: GetSessionProps): string | null => {
   const fromCookie = getFromCookie(headers, clientId);
 
-  return fromCookie || "";
+  return fromCookie || null;
 };
 

 export const getSession = ({ headers, clientId }: GetSessionProps): string => {
+  if (!clientId || typeof clientId !== 'string') {
+    throw new Error('Invalid clientId provided');
+  }
   const fromCookie = getFromCookie(headers, clientId);
 
   return fromCookie || "";
 };