Getting strange behavior when calling function outside of a closure:
I had a similar experience.
The error was triggered when I initialize a variable on the driver (master), but then tried to use it on one of the workers. When that happens, Spark Streaming will try to serialize the object to send it over to the worker, and fail if the object is not serializable.
I solved the error by making the variable static.
Previous non-working code
private final PhoneNumberUtil phoneUtil = PhoneNumberUtil.getInstance();
Working code
private static final PhoneNumberUtil phoneUtil = PhoneNumberUtil.getInstance();
Credits: