* {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {
    return Absent.withType();
  }

  /**
   * Returns an {@code Optional} instance containing the given non-null reference. To have {@code
   * null} treated as {@link #absent}, use {@link #fromNullable} instead.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> no differences.
   *

    // Exists to test that our framework doesn't run it:
    @SuppressWarnings("unused")
    @ExampleBaseFeature.Require(absent = {ExampleBaseFeature.BASE_FEATURE_1})
    public void testRequiringConflictingFeatures() throws Exception {
      doNotActuallyRunThis();
    }
  }

  @ExampleDerivedFeature.Require(absent = {ExampleDerivedFeature.DERIVED_FEATURE_2})
  private static class ConflictingRequirementsExampleDerivedInterfaceTester

    // Exists to test that our framework doesn't run it:
    @SuppressWarnings("unused")
    @ExampleBaseFeature.Require(absent = {ExampleBaseFeature.BASE_FEATURE_1})
    public void testRequiringConflictingFeatures() throws Exception {
      doNotActuallyRunThis();
    }
  }

  @ExampleDerivedFeature.Require(absent = {ExampleDerivedFeature.DERIVED_FEATURE_2})
  private static class ConflictingRequirementsExampleDerivedInterfaceTester

       *
       * The absent indicator of -1 signed becomes 2^8 - 1 unsigned, which reduces the actual max
       * size to 2^8 - 1. However, due to a load factor < 1 the limit is never approached.
       */
      byte[] hashTable = new byte[tableSize];
      Arrays.fill(hashTable, ABSENT);

      int outI = 0;
      entries:
      for (int i = 0; i < n; i++) {

    Set<Feature<?>> moreAbsentFeatures = moreRequirements.getAbsentFeatures();
    checkConflict("absent", absentFeatures, "present", morePresentFeatures, source);
    checkConflict("present", presentFeatures, "absent", moreAbsentFeatures, source);
    presentFeatures.addAll(morePresentFeatures);
    absentFeatures.addAll(moreAbsentFeatures);
    return requirements;
  }

    Set<Feature<?>> moreAbsentFeatures = moreRequirements.getAbsentFeatures();
    checkConflict("absent", absentFeatures, "present", morePresentFeatures, source);
    checkConflict("present", presentFeatures, "absent", moreAbsentFeatures, source);
    presentFeatures.addAll(morePresentFeatures);
    absentFeatures.addAll(moreAbsentFeatures);
    return requirements;
  }

   *
   * - Define putIfAbsent and replace as treating zero and absent identically (as currently
   *   implemented below). This is a bit surprising with putIfAbsent, which really becomes
   *   putIfZero.
   *
   * - Allow putIfAbsent and replace to distinguish between zero and absent, but don't implement
   *   remove(K, long). Without any two-phase operations it becomes feasible for all remaining

   * Returns the size of this source in bytes, if the size can be easily determined without actually
   * opening the data stream.
   *
   * <p>The default implementation returns {@link Optional#absent}. Some sources, such as a file,
   * may return a non-absent value. Note that in such cases, it is <i>possible</i> that this method
   * will return a different number of bytes than would be returned by reading all of the bytes (for

        com.google.common.base.Optional.absent(),
        generator.generateFresh(new TypeToken<com.google.common.base.Optional<String>>() {}));
    assertEquals(
        com.google.common.base.Optional.of("2"),
        generator.generateFresh(new TypeToken<com.google.common.base.Optional<String>>() {}));
    // Test that the first generated instance for different cgcb.Optional<T> is always absent().

        com.google.common.base.Optional.absent(),
        generator.generateFresh(new TypeToken<com.google.common.base.Optional<String>>() {}));
    assertEquals(
        com.google.common.base.Optional.of("2"),
        generator.generateFresh(new TypeToken<com.google.common.base.Optional<String>>() {}));
    // Test that the first generated instance for different cgcb.Optional<T> is always absent().