apache/flink · error · InvalidTypesException

Type extraction is not possible on Either type as it does…

Error message

Type extraction is not possible on Either type as it does not contain information about the 'right' type.

What it means

Thrown by EitherTypeInfoFactory.createTypeInfo() when the 'R' (Right type) of Either<L,R> could not be resolved during type extraction. Mirror of the 'L' case: if either side is missing the factory aborts to avoid an unsound type information.

Solutions

1. Supply explicit type hints via .returns(TypeInformation.of(new TypeHint<Either<L,R>>(){})).
2. Ensure the Right type is a concrete, inferable class in the function signature.
3. Replace Either with a tuple/POJO if both types cannot be statically known.

Example fix

// before
DataStream<Either<String,?>> out = in.map(this::classify); // R unknown

// after
DataStream<Either<String,Integer>> out = in
  .map(this::classify)
  .returns(TypeInformation.of(new TypeHint<Either<String,Integer>>(){}));

TypeInformation<Either<L, R>> ti =
    TypeInformation.of(new TypeHint<Either<L, R>>(){});

static <L,R> TypeInformation<Either<L,R>> eitherTi(Class<L> l, Class<R> r) {
    return new EitherTypeInfo<>(TypeInformation.of(l), TypeInformation.of(r));
}

When it happens

Trigger: Using Either<L,R> with an inferable left but an erased/unknown right type; the Right branch is never used concretely so the extractor cannot bind R.

Common situations: A function returns Either but only one side is referenced concretely; subclassing or raw usage of Either; type erasure in a generic wrapper around Either.

Related errors

• Type extraction is not possible on Either type as it does…
• Cannot convert type to class
• Cannot extract the type argument with index
• Could not create TypeInformation for type
• The generic type parameters of

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/8967daff5b5e5bae. Report an issue: GitHub.

Appendix: source

Thrown at flink-core/src/main/java/org/apache/flink/api/java/typeutils/EitherTypeInfoFactory.java:44

import java.lang.reflect.Type;
import java.util.Map;

public class EitherTypeInfoFactory<L, R> extends TypeInfoFactory<Either<L, R>> {

    @Override
    public TypeInformation<Either<L, R>> createTypeInfo(
            Type t, Map<String, TypeInformation<?>> genericParameters) {
        TypeInformation<?> leftType = genericParameters.get("L");
        TypeInformation<?> rightType = genericParameters.get("R");

        if (leftType == null) {
            throw new InvalidTypesException(
                    "Type extraction is not possible on Either"
                            + " type as it does not contain information about the 'left' type.");
        }

        if (rightType == null) {
            throw new InvalidTypesException(
                    "Type extraction is not possible on Either"
                            + " type as it does not contain information about the 'right' type.");
        }

        return new EitherTypeInfo(leftType, rightType);
    }
}

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