---

## Migration Checklist

Use this checklist to ensure a complete migration:

### Pre-Migration

- [ ] Assess current search system (document count, size, sources)
- [ ] Review infrastructure requirements
- [ ] Install and configure Fess (version: ______)
- [ ] Install compatible OpenSearch/Elasticsearch
- [ ] Backup current search system configuration
- [ ] Backup current search indices/documents

   * navigable set is accomplished through the returned navigable set (or its views).
   *
   * <p>It is imperative that the user manually synchronize on the returned sorted set when
   * iterating over it or any of its {@code descendingSet}, {@code subSet}, {@code headSet}, or
   * {@code tailSet} views.
   *
   * {@snippet :
   * NavigableSet<E> set = synchronizedNavigableSet(new TreeSet<E>());

            countMap.remove(element, existingCounter);
          }
          return true;
        }
      }
    }
    return false;
  }

  // Views

  @Override
  Set<E> createElementSet() {
    Set<E> delegate = countMap.keySet();
    return new ForwardingSet<E>() {
      @Override
      protected Set<E> delegate() {
        return delegate;

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import java.util.RandomAccess;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import org.jspecify.annotations.Nullable;

/**
 * Synchronized collection views. The returned synchronized collection views are serializable if the
 * backing collection and the mutex are serializable.
 *
 * <p>If {@code null} is passed as the {@code mutex} parameter to any of this class's top-level

import java.util.function.UnaryOperator;
import java.util.stream.Stream;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

/**
 * Synchronized collection views. The returned synchronized collection views are serializable if the
 * backing collection and the mutex are serializable.
 *
 * <p>If {@code null} is passed as the {@code mutex} parameter to any of this class's top-level

  @Override
  public boolean containsValue(@Nullable Object value) {
    return value != null && super.containsValue(value);
  }

  @Override
  public int size() {
    return size;
  }

  // views

  /**
   * Returns an immutable set of the distinct keys in this multimap, in the same order as they
   * appear in this multimap.
   */
  @Override
  public ImmutableSet<K> keySet() {

                "- change formatting or whitespace unless absolutely required.",
                "Only change what must be changed. The goal is to minimize diffs for easier human review.",

 * <ul>
 *   <li>Use a provided converter implementation, such as {@link Enums#stringConverter}, {@link
 *       com.google.common.primitives.Ints#stringConverter Ints.stringConverter} or the {@linkplain
 *       #reverse reverse} views of these.
 *   <li>Convert between specific preset values using {@link
 *       com.google.common.collect.Maps#asConverter Maps.asConverter}. For example, use this to

  @Override
  public boolean containsValue(@Nullable Object value) {
    return value != null && super.containsValue(value);
  }

  @Override
  public int size() {
    return size;
  }

  // views

  /**
   * Returns an immutable set of the distinct keys in this multimap, in the same order as they
   * appear in this multimap.
   */
  @Override
  public ImmutableSet<K> keySet() {