this.lastmod = lastmod;
    }

    /**
     * Returns the change frequency of this sitemap entry.
     * @return the change frequency
     */
    public String getChangefreq() {
        return changefreq;
    }

    /**
     * Sets the change frequency of this sitemap entry.
     * @param changefreq the change frequency to set
     */
    public void setChangefreq(final String changefreq) {

      checkArgument(occurrences >= 0);
      Integer frequency = backingMap.getOrDefault(element, 0);
      if (occurrences == 0) {
        return frequency;
      }
      checkArgument(occurrences <= Integer.MAX_VALUE - frequency);
      backingMap.put(element, frequency + occurrences);
      return frequency;
    }

    @Override
    Iterator<E> elementIterator() {

    assertEquals(1, frequency(set, "a"));
    assertEquals(1, frequency(set, "b"));
    assertEquals(1, frequency(set, "c"));
    assertEquals(0, frequency(set, "d"));
    assertEquals(0, frequency(set, 4.2));
    assertEquals(0, frequency(set, null));
  }

  public void testFrequency_list() {
    List<String> list = newArrayList("a", "b", "a", "c", "b", "a");
    assertEquals(3, frequency(list, "a"));

 * <li>{@link #READING_PREFIX} - The prefix for reading fields.</li>
 * <li>{@link #SCORE} - The score field.</li>
 * <li>{@link #QUERY_FREQ} - The query frequency field.</li>
 * <li>{@link #DOC_FREQ} - The document frequency field.</li>
 * <li>{@link #USER_BOOST} - The user boost field.</li>
 * <li>{@link #KINDS} - The kinds field.</li>
 * <li>{@link #TIMESTAMP} - The timestamp field.</li>

        request.addExcludeWord(excludeWord);
        return this;
    }

    /**
     * Sets the query frequency threshold.
     * @param queryFreqThreshold The query frequency threshold.
     * @return This builder instance.
     */
    public PopularWordsRequestBuilder setQueryFreqThreshold(final int queryFreqThreshold) {

    assertEquals(1, frequency(set, "a"));
    assertEquals(1, frequency(set, "b"));
    assertEquals(1, frequency(set, "c"));
    assertEquals(0, frequency(set, "d"));
    assertEquals(0, frequency(set, 4.2));
    assertEquals(0, frequency(set, null));
  }

  public void testFrequency_list() {
    List<String> list = newArrayList("a", "b", "a", "c", "b", "a");
    assertEquals(3, frequency(list, "a"));

        return kinds;
    }

    /**
     * Returns the query frequency of the suggest item.
     * @return The query frequency.
     */
    public long getQueryFreq() {
        return queryFreq;
    }

    /**
     * Returns the document frequency of the suggest item.
     * @return The document frequency.
     */
    public long getDocFreq() {
        return docFreq;
    }

        this.responseSequenceNumber = responseSequenceNumber;
    }

    /**
     * Gets the heartbeat interval recommended by the server (in milliseconds).
     * The client can use this to adjust the heartbeat frequency.
     *
     * @return the heartbeat interval in milliseconds
     */
    public long getHeartbeatInterval() {
        return heartbeatInterval;
    }

    /**
     * Sets the heartbeat interval.

    List<@Nullable String> list = newArrayList("a", null, "b", null, "a", null);
    assertEquals(2, frequency(list.iterator(), "a"));
    assertEquals(1, frequency(list.iterator(), "b"));
    assertEquals(0, frequency(list.iterator(), "c"));
    assertEquals(0, frequency(list.iterator(), 4.2));
    assertEquals(3, frequency(list.iterator(), null));
  }

  @GwtIncompatible // slow (~4s)

     */
    public void addExcludeWord(final String excludeWord) {
        excludeWords.add(excludeWord);
    }

    /**
     * Sets the query frequency threshold.
     * @param queryFreqThreshold The query frequency threshold.
     */
    public void setQueryFreqThreshold(final int queryFreqThreshold) {
        this.queryFreqThreshold = queryFreqThreshold;
    }

    @Override