AuthTokenDto: Make properties consistently optional

validUntil and lastUsed already have a IsOptional decorator,
this makes the properties themselves also optional

Signed-off-by: David Mehren <git@herrmehren.de>

src/auth/auth-token.dto.ts

@@ -15,8 +15,8 @@ export class AuthTokenDto {
   createdAt: Date;
   @IsDate()
   @IsOptional()
-  validUntil: Date;
+  validUntil: Date | null;
   @IsDate()
   @IsOptional()
-  lastUsed: Date;
+  lastUsed: Date | null;
 }