apache/beam · error · RuntimeException

Internal error: unexpected kind of Type:

Error message

Internal error: unexpected kind of Type: 

What it means

getCoderFromTypeDescriptor dispatches on the kind of java.lang.reflect.Type it received (Class, ParameterizedType, TypeVariable, WildcardType). If the Type is none of these known kinds, an internal invariant is violated and the registry throws a bare RuntimeException labelled as an internal error. This should be unreachable in normal use and usually signals a nonstandard Type implementation.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/coders/CoderRegistry.java:638

            String.format(
                "Cannot provide a coder for type variable %s"
                    + " because the actual type is over specified by multiple"
                    + " incompatible coders %s.",
                type, coders),
            ReasonCode.OVER_SPECIFIED);
      }
    } else if (type instanceof Class<?>) {
      coder = getCoderFromFactories(typeDescriptor, Collections.emptyList());
    } else if (type instanceof ParameterizedType) {
      coder = getCoderFromParameterizedType((ParameterizedType) type, typeCoderBindings);
    } else if (type instanceof TypeVariable) {
      coder = getCoderFromFactories(typeDescriptor, Collections.emptyList());
    } else if (type instanceof WildcardType) {
      // No coder for an unknown generic type.
      throw new CannotProvideCoderException(
          String.format("Cannot provide a coder for wildcard type %s.", type), ReasonCode.UNKNOWN);
    } else {
      throw new RuntimeException("Internal error: unexpected kind of Type: " + type);
    }

    LOG.debug("Coder for {}: {}", typeDescriptor, coder);
    @SuppressWarnings("unchecked")
    Coder<T> result = (Coder<T>) coder;
    return result;
  }

  /**
   * Returns a {@link Coder} to use for values of the given parameterized type, in a context where
   * the given types use the given {@link Coder Coders}.
   *
   * @throws CannotProvideCoderException if no coder can be provided
   */
  private Coder<?> getCoderFromParameterizedType(
      ParameterizedType type, SetMultimap<Type, Coder<?>> typeCoderBindings)
      throws CannotProvideCoderException {

View on GitHub (pinned to 12126d8942)

Solutions

1. Inspect and log the offending Type object's class to identify where the nonstandard Type comes from.
2. Replace custom Type implementations with standard JDK Class/ParameterizedType instances when building TypeDescriptors.
3. Update/patch Apache Beam if the Type was produced by Beam itself (report the bug).

Example fix

// before
TypeDescriptor<T> td = TypeDescriptor.of(myCustomTypeImpl);
// after
TypeDescriptor<T> td = TypeDescriptor.of(ConcreteClass.class);

Type t = typeDescriptor.getType();
if (!(t instanceof Class || t instanceof ParameterizedType
    || t instanceof TypeVariable || t instanceof WildcardType)) {
  throw new IllegalArgumentException("Nonstandard Type: " + t.getClass());
}

static boolean isStandardReflectType(Type t) {
  return t instanceof Class || t instanceof ParameterizedType
      || t instanceof TypeVariable || t instanceof WildcardType;
}

try {
  coder = registry.getCoder(td);
} catch (RuntimeException e) {
  if (e.getMessage().startsWith("Internal error: unexpected kind of Type")) {
    // log td.getType().getClass() and fix Type construction
  }
}

When it happens

Trigger: Passing a Type object that is not Class, ParameterizedType, TypeVariable, or WildcardType — typically a custom/unusual Type implementation or a corrupt descriptor produced by other reflection code — into getCoder/getDefaultCoders.

Common situations: Third-party reflection libraries returning exotic Type implementations; bug in code constructing TypeDescriptor objects; Beam internal invariant breakage after library upgrade.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• error when invoking Coder factory method
• cannot register Coder : does not have an accessible method n
• cannot register Coder : method named 'of' with arguments of
• cannot register Coder : method named 'of' with arguments of
• cannot register Coder : method named 'of' with arguments of

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/0f0364b3ed326b2d. Report an issue: GitHub.