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The public API for JIRA REST Java Client

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package com.atlassian.jira.rest.client.api;

import javax.annotation.Nullable;
import java.util.Collections;
import java.util.Iterator;

/**
 * Represent iterable which is optional (for example due to lack of field in old REST API version).

 * This iterable is intended to be not null, so you can always get items by using iterator. If you need
 * to check if value was actually provided then use {@link OptionalIterable#isSupported}.
 *
 * @since v1.0
 */
public class OptionalIterable implements Iterable {

	@SuppressWarnings("unchecked")
	private static final OptionalIterable absentInstance = new OptionalIterable(null);

	@Nullable
	private final Iterable iterable;

	@SuppressWarnings("unchecked")
	public static  OptionalIterable absent() {
		return absentInstance;
	}

	public OptionalIterable(@Nullable Iterable iterable) {
		this.iterable = iterable;
	}

	/**
	 * @return iterator for original iterable if {@link OptionalIterable#isSupported} is true,
	 *         or empty iterator in other case.
	 */
	@Override
	public Iterator iterator() {
		return isSupported()
				? iterable.iterator()
				: Collections.emptyList().iterator();
	}

	/**
	 * @return true if server supports this field
	 */
	public boolean isSupported() {
		return iterable != null;
	}

    @Override
    public String toString() {
        return isSupported() ? iterable.toString() : Collections.emptyList().toString();
    }
}