diff --git a/src/auth/auth.service.spec.ts b/src/auth/auth.service.spec.ts
index b79f7f0bf..ab13f1141 100644
--- a/src/auth/auth.service.spec.ts
+++ b/src/auth/auth.service.spec.ts
@@ -319,4 +319,10 @@ describe('AuthService', () => {
       );
     });
   });
+  describe('randomString', () => {
+    it('throws on invalid lenght parameter', () => {
+      expect(() => service.randomString(0)).toThrow();
+      expect(() => service.randomString(-1)).toThrow();
+    });
+  });
 });
diff --git a/src/auth/auth.service.ts b/src/auth/auth.service.ts
index 76758e680..45fa70280 100644
--- a/src/auth/auth.service.ts
+++ b/src/auth/auth.service.ts
@@ -64,7 +64,7 @@ export class AuthService {
 
   randomString(length: number): Buffer {
     if (length <= 0) {
-      return null;
+      throw new Error('randomString cannot have a length < 1');
     }
     return randomBytes(length);
   }