Generating null values

By default, generated values are never null. One possible way to generate an optional value of type T in Java is to declare a parameter of type Optional<T>.

However, in some cases it preferable to generate values that can include null. For example, Kotlin’s type system explicitly manages nullable types and therefore Kotlin programs use nullable types like T? instead of Optional<T> to indicate that a value may be absent.

In order to generate null values, attach the JSR 303 javax.annotation.Nullable annotation to a parameter of any supported type:

    @RunWith(JUnitQuickcheck.class)
    public class NullableParameterProperties {
        @Property public void validPhoneNumber(@Nullable String areaCode, String lineNumber) {
            // ...
        }
    }

Alternatively, use the annotation @NullAllowed introduced by junit-quickcheck, which makes it possible to indicate the probability of generating a null value:

    @RunWith(JUnitQuickcheck.class)
    public class NullableParameterProperties {
        @Property public void validPhoneNumber(@NullAllowed(probability = 0.8f) String areaCode, String lineNumber) {
            // ...
        }
    }