# Exceptions - `HTTPException` and `WebSocketException`

These are the exceptions that you can raise to show errors to the client.

When you raise an exception, as would happen with normal Python, the rest of the execution is aborted. This way you can raise these exceptions from anywhere in the code to abort a request and show the error to the client.

You can use:

* `HTTPException`
* `WebSocketException`

     * @return The version result, never {@code null}.
     * @throws VersionResolverException If the metaversion could not be resolved.
     */
    @Nonnull
    default VersionResolverResult resolve(@Nonnull Session session, @Nonnull ArtifactCoordinates artifactCoordinates)
            throws VersionResolverException {

   * Returns the result of adding this and {@code val}. If the result would have more than 32 bits,
   * returns the low 32 bits of the result.
   *
   * @since 14.0
   */
  public UnsignedInteger plus(UnsignedInteger val) {
    return fromIntBits(this.value + checkNotNull(val).value);
  }

  /**
   * Returns the result of subtracting this and {@code val}. If the result would be negative,
   * returns the low 32 bits of the result.

    return backingMap;
  }

  @SuppressWarnings("unchecked") // value could not get in if not a T
  private <T extends B> @Nullable T trustedPut(
      TypeToken<@NonNull T> type, @ParametricNullness T value) {
    return (T) backingMap.put(type, value);
  }

  @SuppressWarnings("unchecked") // value could not get in if not a T
  private <T extends @NonNull B> @Nullable T trustedGet(TypeToken<T> type) {

      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_KEY_QUERIES)
  public void testReplace_absentNullKeyUnsupported() {
    try {
      getMap().replace(null, v3());
    } catch (NullPointerException tolerated) {
      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

Import `Form` from `fastapi`:

{* ../../docs_src/request_forms/tutorial001_an_py39.py hl[3] *}

## Define `Form` parameters { #define-form-parameters }

Create form parameters the same way you would for `Body` or `Query`:

{* ../../docs_src/request_forms/tutorial001_an_py39.py hl[9] *}

   * Returns the result of adding this and {@code val}. If the result would have more than 64 bits,
   * returns the low 64 bits of the result.
   *
   * @since 14.0
   */
  public UnsignedLong plus(UnsignedLong val) {
    return fromLongBits(this.value + checkNotNull(val).value);
  }

  /**
   * Returns the result of subtracting this and {@code val}. If the result would have more than 64
   * bits, returns the low 64 bits of the result.

        }

        final ExtractorFactory extractorFactory = crawlerContainer.getComponent("extractorFactory");
        if (extractorFactory == null) {
            throw new CrawlerSystemException("Could not find extractorFactory.");
        }
        final Extractor extractor = extractorFactory.getExtractor(responseData.getMimeType());
        final Map<String, String> params = new HashMap<>();

    return backingMap;
  }

  @SuppressWarnings("unchecked") // value could not get in if not a T
  private <T extends B> @Nullable T trustedPut(
      TypeToken<@NonNull T> type, @ParametricNullness T value) {
    return (T) backingMap.put(type, value);
  }

  @SuppressWarnings("unchecked") // value could not get in if not a T
  private <T extends @NonNull B> @Nullable T trustedGet(TypeToken<T> type) {

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Optimization (provides speedup with no functional changes)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Checklist:
- [ ] Fixes a regression (If yes, please add `commit-id` or `PR #` here)
- [ ] Unit tests added/updated
- [ ] Internal documentation updated