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/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package reactor.util.annotation;

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

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

/**
 * A common Reactor annotation (similar to Spring ones) to declare that annotated elements
 * can be {@code null} under some circumstance. Leverages JSR 305 meta-annotations to
 * indicate nullability in Java to common tools with JSR 305 support and used by Kotlin to
 * infer nullability of Reactor API.
 *
 * Should be used at parameter, return value, and field level.
 * Methods overrides should repeat parent {@code @Nullable} annotations unless they behave
 * differently.
 *
 * Can be used in association with {@code NonNullApi} to override the default
 * non-nullable semantic to nullable.
 *
 * @author Sebastien Deleuze
 * @author Juergen Hoeller
 * @since 3.1.0
 * @see NonNullApi
 * @see NonNull
 */
@Target({ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Nonnull(when = When.MAYBE)
@TypeQualifierNickname
public @interface Nullable {
}