{* ../../docs_src/query_params_str_validations/tutorial006_an_py310.py hl[9] *}

### Required, can be `None` { #required-can-be-none }

You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.

To do that, you can declare that `None` is a valid type but simply do not declare a default value:

		return
	}

	var forceMD5 []byte
	// Optimization: If SSE-KMS and SSE-C did not request Content-Md5. Use uuid as etag. Optionally enable this also
	// for server that is started with `--no-compat`.
	kind, _ := crypto.IsRequested(formValues)
	if !etag.ContentMD5Requested(formValues) && (kind == crypto.SSEC || kind == crypto.S3KMS || !globalServerCtxt.StrictS3Compat) {
		forceMD5 = mustGetUUIDBytes()
	}

          return rest[index - 2];
      }
    }

    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
  }

  /**
   * Returns every possible list that can be formed by choosing one element from each of the given
   * lists in order; the "n-ary <a href="http://en.wikipedia.org/wiki/Cartesian_product">Cartesian
   * product</a>" of the lists. For example:
   *
   * {@snippet :

		d.deleteRecursive(candidate)
		d.replaceHashed(candidate, nil, *flat)

		// Remove top entry and subtract removed children.
		remove -= removing
		leaves = leaves[1:]
	}
}

// forceCompact will force compact the cache of the top entry.
// If the number of children is more than limit*100, it will compact self.
// When above the limit a cleanup will also be performed to remove any possible abandoned entries.

        });
        indexUpdater.start();

        int startedCrawlerNum = 0;
        int activeCrawlerNum = 0;
        try {
            while (startedCrawlerNum < crawlerList.size()) {
                // Force to stop crawl
                if (systemHelper.isForceStop()) {
                    for (final Crawler crawler : crawlerList) {
                        crawler.stop();
                    }
                    break;

                  @Override
                  protected Set<String> create(String[] elements) {
                    ImmutableSet.Builder<String> builder = ImmutableSet.builder();
                    builder.forceJdk();
                    builder.add(elements);
                    return builder.build();
                  }
                })
            .named(ImmutableSetTest.class.getName() + ", with JDK builder")

        assertTrue(result >= 8);
        assertNotNull(response.getResults());
    }

    @Test
    @DisplayName("Test readBytesWireFormat with properly formed empty response")
    void testReadBytesWireFormatProperlyFormedEmpty() throws Exception {
        response = new Smb2QueryDirectoryResponse(mockConfig, Smb2QueryDirectoryRequest.FILE_BOTH_DIRECTORY_INFO);

		case c == '"':
			return string(d.scratch.bytes()), nil
		case c == '\\':
			c = d.next()
			goto scan_esc
		case c < 0x20:
			return "", d.mkError(ErrSyntax, "in string literal")
		// Coerce to well-formed UTF-8.
		default:
			d.scratch.add(c)
			if d.remaining() == 0 {
				return "", d.mkError(ErrSyntax, "in string literal")
			}
			c = d.next()
		}
	}

scan_esc:
	switch c {

    assertThrows(IllegalArgumentException.class, () -> ImmutableIntArray.builder(-1));
  }

  /**
   * If there's a bug in builder growth, we wouldn't know how to expose it. So, brute force the hell
   * out of it for a while and see what happens.
   */
  public void testBuilder_bruteForce() {
    for (int i = 0; i < reduceIterationsIfGwt(100); i++) {

    assertThrows(IllegalArgumentException.class, () -> ImmutableDoubleArray.builder(-1));
  }

  /**
   * If there's a bug in builder growth, we wouldn't know how to expose it. So, brute force the hell
   * out of it for a while and see what happens.
   */
  public void testBuilder_bruteForce() {
    for (int i = 0; i < reduceIterationsIfGwt(100); i++) {