return asList(elements).iterator();
  }

  // In GWT, java.util.TreeSet throws ClassCastException when the comparator
  // throws it, unlike the JDK.  Therefore, we accept ClassCastException as a
  // valid result thrown by java.util.TreeSet#equals.
  private static void assertNotEqualLenient(TreeSet<?> unexpected, SortedSet<?> actual) {
    try {
      assertThat(actual).isNotEqualTo(unexpected);

       * only if this iterator passed across threads,
       * which we don't support anyway.
       */
      return nextIndex >= 0;
    }

    /**
     * Checks whether nextIndex is valid; if so setting nextItem. Stops iterator when either hits
     * putIndex or sees null item.
     */
    private void checkNext() {
      if (nextIndex == putIndex) {
        nextIndex = -1;
        nextItem = null;

        </field>
        <field>
          <name>checksumPolicy</name>
          <version>1.0.0+</version>
          <description>
            What to do when verification of an artifact checksum fails. Valid values are "fail" (default for Maven 4 and
            above), "warn" (default for Maven 3) or "ignore".
          </description>
          <type>String</type>
        </field>
      </fields>
    </class>

		jbytes, err := json.Marshal(healSequenceStatus{
			Summary: healFinishedStatus,
		})
		return jbytes, toAdminAPIErrCode(GlobalContext, err)
	}

	// Check if client-token is valid
	if clientToken != h.clientToken {
		return nil, ErrHealInvalidClientToken
	}

	// Take lock to access and update the heal-sequence
	h.mutex.Lock()
	defer h.mutex.Unlock()

          escapedInput.append(c);
        } else {
          escapedInput.append(String.format("\\u%04x", (int) c));
        }
      }
      fail("FLOATING_POINT_PATTERN should have matched valid input <" + escapedInput + ">");
    }
  }

  @GwtIncompatible // Doubles.tryParse
  private static void checkTryParse(double expected, String input) {

      assertTrue(
          LongMath.biggestBinomials[k] == Integer.MAX_VALUE
              || !fitsInLong(BigIntegerMath.binomial(LongMath.biggestBinomials[k] + 1, k)));
      // In the first case, any long is valid; in the second, we want to test that the next-bigger
      // long overflows.
    }
    int k = LongMath.biggestBinomials.length;
    assertFalse(fitsInLong(BigIntegerMath.binomial(2 * k, k)));

            UpgradeResult result = strategy.apply(context, pomMap);

            // Should succeed
            assertTrue(result.success(), "Valid upgrade should be successful");
            assertEquals(0, result.errorCount(), "Should have no errors");
            assertEquals(1, result.modifiedCount(), "Should have modified one POM");
        }
    }

      WrappedIterator(Iterator<V> delegateIterator) {
        this.delegateIterator = delegateIterator;
      }

      /**
       * If the delegate changed since the iterator was created, the iterator is no longer valid.
       */
      void validateIterator() {
        refreshIfEmpty();
        if (delegate != originalDelegate) {
          throw new ConcurrentModificationException();
        }
      }

Another big feature needed by APIs is data validation, making sure that the data is valid, given certain parameters. For example, that some field is an `int`, and not some random string. This is especially useful for incoming data.

Without a data validation system, you would have to do all the checks by hand, in code.

              <a href="http://en.wikipedia.org/wiki/UTC%E2%88%9212:00">-12</a> to <a href="http://en.wikipedia.org/wiki/UTC%2B14:00">+14</a>
              or a valid time zone id like "America/Montreal" (UTC-05:00) or "Europe/Paris" (UTC+01:00).
            ]]>
          </description>
          <type>String</type>
        </field>
        <field>