/*
 * Copyright (C) 2015, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.annotations;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;

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

Marks types that can hold the value null at run time. 
 Unlike org.eclipse.jdt.annotation.Nullable, this has run-time retention, allowing the annotation to be recognized by Guice. Unlike javax.annotation.Nullable, this does not involve importing new classes to a standard (Java EE) package, so it can be deployed in an OSGi container without running into split-package
problems.
 You can use this annotation to qualify a type in a method signature or local variable declaration. The entity whose type has this annotation is allowed to hold the value null at run time. This allows annotation based null analysis to infer that 

Binding a null value to the entity is legal. 
Dereferencing the entity is unsafe and can trigger a NullPointerException. 
 To avoid a dependency on Java 8, this annotation does not use @Target TYPE_USE. That may change when JGit starts requiring Java 8. 

Warning: Please do not use this annotation on arrays. Different annotation processors treat @Nullable Object[] differently: some treat it as an array of nullable objects, for consistency with versions of Nullable defined with @Target TYPE_USE, while others treat it as a nullable array of objects. JGit therefore avoids using this annotation on arrays altogether. 
See Also:

 *      The checker-framework manual
Since:
4.2/**
 * Marks types that can hold the value {@code null} at run time.
 * <p>
 * Unlike {@code org.eclipse.jdt.annotation.Nullable}, this has run-time
 * retention, allowing the annotation to be recognized by
 * <a href="https://github.com/google/guice/wiki/UseNullable">Guice</a>. Unlike
 * {@code javax.annotation.Nullable}, this does not involve importing new classes
 * to a standard (Java EE) package, so it can be deployed in an OSGi container
 * without running into
 * <a href="http://wiki.osgi.org/wiki/Split_Packages">split-package</a>
 * <a href="https://gerrit-review.googlesource.com/50112">problems</a>.
 * <p>
 * You can use this annotation to qualify a type in a method signature or local
 * variable declaration. The entity whose type has this annotation is allowed to
 * hold the value {@code null} at run time. This allows annotation based null
 * analysis to infer that
 * <ul>
 * <li>Binding a {@code null} value to the entity is legal.
 * <li>Dereferencing the entity is unsafe and can trigger a
 * {@code NullPointerException}.
 * </ul>
 * <p>
 * To avoid a dependency on Java 8, this annotation does not use
 * {@link Target @Target} {@code TYPE_USE}. That may change when JGit starts
 * requiring Java 8.
 * <p>
 * <b>Warning:</b> Please do not use this annotation on arrays. Different
 * annotation processors treat {@code @Nullable Object[]} differently: some
 * treat it as an array of nullable objects, for consistency with versions of
 * {@code Nullable} defined with {@code @Target} {@code TYPE_USE}, while others
 * treat it as a nullable array of objects. JGit therefore avoids using this
 * annotation on arrays altogether.
 *
 * @see <a href=
 *      "http://types.cs.washington.edu/checker-framework/current/checker-framework-manual.html#faq-array-syntax-meaning">
 *      The checker-framework manual</a>
 * @since 4.2
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ FIELD, METHOD, PARAMETER, LOCAL_VARIABLE })
public @interface Nullable {
	// marker annotation with no members
}