String[] keys = entrySet.stream().map(Map.Entry::getKey).toArray(String[]::new);

        assertTrue("Should contain all keys", Arrays.asList(keys).contains("lang"));
        assertTrue("Should contain all keys", Arrays.asList(keys).contains("a_key"));
        assertTrue("Should contain all keys", Arrays.asList(keys).contains("b_key"));
        assertTrue("Should contain all keys", Arrays.asList(keys).contains("c_key"));

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableSortedMap} whose
   * keys and values are the result of applying the provided mapping functions to the input
   * elements. The generated map is sorted by the natural ordering of the keys.
   *
   * <p>If the mapped keys contain duplicates, an {@code IllegalArgumentException} is thrown when

  }

  /**
   * Associates the value {@code null} with the specified keys, assuming both keys are valid. If
   * either key is null or isn't among the keys provided during construction, this method has no
   * effect.
   *
   * <p>This method is equivalent to {@code put(rowKey, columnKey, null)} when both provided keys
   * are valid.
   *
   * @param rowKey row key of mapping to be erased

      this.keys = new @Nullable Object[initialCapacity];
      this.values = new @Nullable Object[initialCapacity];
    }

    private void ensureCapacity(int minCapacity) {
      if (minCapacity > keys.length) {
        int newCapacity = ImmutableCollection.Builder.expandedCapacity(keys.length, minCapacity);
        this.keys = Arrays.copyOf(keys, newCapacity);

  /**
   * Computes or retrieves the values corresponding to {@code keys}. This method is called by {@link
   * LoadingCache#getAll}.
   *
   * <p>If the returned map doesn't contain all requested {@code keys} then the entries it does
   * contain will be cached, but {@code getAll} will throw an exception. If the returned map
   * contains extra keys not present in {@code keys} then all returned entries will be cached, but

  /**
   * Returns a map of the values associated with {@code keys}, creating or retrieving those values
   * if necessary. The returned map contains entries that were already cached, combined with newly
   * loaded entries; it will never contain null keys or values.
   *
   * <p>Caches loaded by a {@link CacheLoader} will issue a single request to {@link
   * CacheLoader#loadAll} for all keys which are not already present in the cache. All entries

import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * A {@link BiMap} backed by two hash tables. This implementation allows null keys and values. A
 * {@code HashBiMap} and its inverse are both serializable.
 *
 * <p>This implementation guarantees insertion-based iteration order of its keys.
 *
 * <p>See the Guava User Guide article on <a href=

  /**
   * Computes or retrieves the values corresponding to {@code keys}. This method is called by {@link
   * LoadingCache#getAll}.
   *
   * <p>If the returned map doesn't contain all requested {@code keys} then the entries it does
   * contain will be cached, but {@code getAll} will throw an exception. If the returned map
   * contains extra keys not present in {@code keys} then all returned entries will be cached, but

      keys.remove(1);
      keys.remove(2);
      assertThat(keys.remove(null)).isFalse();
      assertThat(keys.remove(6)).isFalse();
      assertThat(keys.remove(-6)).isFalse();
      assertThat(keys.removeAll(asList(null, 0, 15, 1500))).isFalse();
      assertThat(keys.retainAll(asList(null, 0, 15, 1500))).isFalse();
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

You can also declare a body as a `dict` with keys of some type and values of some other type.

This way, you don't have to know beforehand what the valid field/attribute names are (as would be the case with Pydantic models).

This would be useful if you want to receive keys that you don't already know.

---

Another useful case is when you want to have keys of another type (e.g., `int`).