JUnit test fails with NPE when testing validator method

I am working through the following tutorial:

http://docs.spring.io/docs/Spring-MVC-step-by-step/part4.html

I am trying to test the validate method in the class below:

public class PriceIncreaseValidator implements Validator {
    public void validate(Object obj, Errors errors) {
        PriceIncrease pi = (PriceIncrease) obj;
        if (pi == null) {
            errors.rejectValue("percentage", "error.not-specified", null, "Value required.");
        }
........
}

Below is my JUnit test case:

private PriceIncreaseValidator priceIncreaseValidator;
private PriceIncrease priceIncrease;
private Errors errors;

public void testEmptyPriceIncrease() {

    priceIncreaseValidator.validate(priceIncrease, errors); // This is where I get NPE

    assertTrue(errors.hasErrors());
}

So when calling the validate method in my JUnit test case, I get NPE. Both tests and classes compile.

I've tried converting priceIncrease to an object as follows, but still no luck:

Object obj = priceIncrease;
//validate
priceIncreaseValidator.validate(obj, errors);

Any ideas?

As you can see, I'm trying to test if the price increase is not set, which returns an error when calling validate.