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).
    * <p>
   * 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<T> implements Iterable<T> {
  
      @SuppressWarnings("unchecked")
      private static final OptionalIterable absentInstance = new OptionalIterable(null);
  
      @Nullable
      private final Iterable<T> iterable;
  
      @SuppressWarnings("unchecked")
      public static <T> OptionalIterable<T> absent() {
          return absentInstance;
      }
  
      public OptionalIterable(@Nullable Iterable<T> iterable) {
          this.iterable = iterable;
      }
  
      /**
       * @return iterator for original iterable if {@link OptionalIterable#isSupported} is true,
       * or empty iterator in other case.
       */
      @Override
      public Iterator<T> iterator() {
          return isSupported()
                  ? iterable.iterator()
                  : Collections.<T>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();
      }
  }