[issues with the "contributions welcome" label](https://github.com/tensorflow/tensorflow/labels/stat%3Acontributions%20welcome).
These are issues that we believe are particularly well suited for outside
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decide to start on an issue, leave a comment so that other people know that
you're working on it. If you want to help out, but not alone, use the issue

   *
   * <p>When eviction is necessary, the cache evicts entries that are less likely to be used again.
   * For example, the cache may evict an entry because it hasn't been used recently or very often.
   *
   * <p>If {@code maximumSize} is zero, elements will be evicted immediately after being loaded into
   * cache. This can be useful in testing, or to disable caching temporarily.
   *

   * remove()}. Otherwise, all optional operations are supported. Null row keys, columns keys, and
   * values are not supported.
   *
   * <p>Lookups by row key are often faster than lookups by column key, because the data is stored
   * in a {@code Map<R, Map<C, V>>}. A method call like {@code column(columnKey).get(rowKey)} still

public abstract class MultimapBuilder<K0 extends @Nullable Object, V0 extends @Nullable Object> {
  /*
   * Leaving K and V as upper bounds rather than the actual key and value types allows type
   * parameters to be left implicit more often. CacheBuilder uses the same technique.
   */

  private MultimapBuilder() {}

  private static final int DEFAULT_EXPECTED_KEYS = 8;

  /** Uses a hash table to map keys to value collections. */

public abstract class MultimapBuilder<K0 extends @Nullable Object, V0 extends @Nullable Object> {
  /*
   * Leaving K and V as upper bounds rather than the actual key and value types allows type
   * parameters to be left implicit more often. CacheBuilder uses the same technique.
   */

  private MultimapBuilder() {}

  private static final int DEFAULT_EXPECTED_KEYS = 8;

  /** Uses a hash table to map keys to value collections. */

     * {@code [a, b, null, c, d, null, e, null]} sequentially, encoding the topological structure.
     * (Note, however, that the callers of {@code visitNext()} often insert additional iterators
     * into {@code horizon} between calls to {@code visitNext()}. This causes them to receive
     * additional values interleaved with those shown above.)
     */

   * the entry from the Map. If another operation sees a zero in the map, it knows that the entry is
   * about to be removed, so this operation may remove it (often by replacing it with a new
   * AtomicInteger).
   */

  /** The number of occurrences of each element. */
  private final transient ConcurrentMap<E, AtomicInteger> countMap;

  /**

   * - Favor responding to interrupts over timeouts.
   * - System.nanoTime() is expensive enough that we want to call it the minimum required number of
   *   times, typically once before invoking a blocking method. This often requires keeping track of
   *   the first time in a method that nanoTime() has been invoked, for which the special value 0L
   *   is reserved to mean "uninitialized". If timeout is non-positive, then nanoTime need never be

   * the entry from the Map. If another operation sees a zero in the map, it knows that the entry is
   * about to be removed, so this operation may remove it (often by replacing it with a new
   * AtomicInteger).
   */

  /** The number of occurrences of each element. */
  private final transient ConcurrentMap<E, AtomicInteger> countMap;

  /**

for your idea, please open one. It may be that somebody is already working on
it, or that there are particular complexities that you should know about before
starting the implementation. There are often a number of ways to fix a problem
and it is important to find the right approach before spending time on a PR
that cannot be merged.

We add the `help wanted` label to existing GitHub issues for which community