package javax.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

import javax.annotation.meta.TypeQualifierNickname;
import javax.annotation.meta.When;

The annotated element could be null under some circumstances.

In general, this means developers will have to read the documentation to
determine when a null value is acceptable and whether it is necessary to
check for a null value.
 This annotation is useful mostly for overriding a Nonnull annotation. Static analysis tools should generally treat the annotated items as though they had no annotation, unless they are configured to minimize false negatives. Use CheckForNull to indicate that the element value should always be checked for a null value. 

When this annotation is applied to a method it applies to the method return value.
/**
 * The annotated element could be null under some circumstances.
 * <p>
 * In general, this means developers will have to read the documentation to
 * determine when a null value is acceptable and whether it is necessary to
 * check for a null value.
 * <p>
 * This annotation is useful mostly for overriding a {@link Nonnull} annotation.
 * Static analysis tools should generally treat the annotated items as though they
 * had no annotation, unless they are configured to minimize false negatives.
 * Use {@link CheckForNull} to indicate that the element value should always be checked
 * for a null value.
 * <p>
 * When this annotation is applied to a method it applies to the method return value.
 */
@Documented
@TypeQualifierNickname
@Nonnull(when = When.UNKNOWN)
@Retention(RetentionPolicy.RUNTIME)
public @interface Nullable {

}