apache/beam · error · RuntimeException

Null value found for field that doesn't support nulls.

Error message

Null value found for field that doesn't support nulls.

What it means

fieldValueToProto converts an in-memory Row field value into its proto representation. Beam requires that a non-nullable field always carry a value; if the value is null and fieldType.getNullable() is false, this RuntimeException is thrown rather than silently encoding a null into a field the schema says cannot be null.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SchemaTranslation.java:580

    return builder.build();
  }

  public static Object rowFromProto(SchemaApi.Row row, FieldType fieldType) {
    Row.Builder builder = Row.withSchema(fieldType.getRowSchema());
    for (int i = 0; i < row.getValuesCount(); ++i) {
      builder.addValue(
          fieldValueFromProto(fieldType.getRowSchema().getField(i).getType(), row.getValues(i)));
    }
    return builder.build();
  }

  static SchemaApi.FieldValue fieldValueToProto(FieldType fieldType, Object value) {
    FieldValue.Builder builder = FieldValue.newBuilder();
    if (value == null) {
      if (fieldType.getNullable()) {
        return builder.build();
      } else {
        throw new RuntimeException("Null value found for field that doesn't support nulls.");
      }
    }

    switch (fieldType.getTypeName()) {
      case ARRAY:
        return builder
            .setArrayValue(
                arrayValueToProto(fieldType.getCollectionElementType(), (Iterable) value))
            .build();
      case ITERABLE:
        return builder
            .setIterableValue(
                iterableValueToProto(fieldType.getCollectionElementType(), (Iterable) value))
            .build();
      case MAP:
        return builder
            .setMapValue(
                mapToProto(fieldType.getMapKeyType(), fieldType.getMapValueType(), (Map) value))

View on GitHub (pinned to 12126d8942)

Solutions

1. Fix the data: ensure every non-nullable field has a value before converting (validate or fill defaults).
2. Mark the field nullable in the Schema (FieldType nullable(true)) if nulls are legitimate.
3. Add a pre-conversion null check that substitutes defaults or fails fast with a clearer message.
4. Trace which pipeline stage produced the invalid Row and add a DoFn-level validation there.

Example fix

// before
FieldType fieldType = FieldType.STRING; // non-nullable, row value is null
// after
FieldType fieldType = FieldType.STRING.withNullable(true);

for (Field f : schema.getFields()) { if (!f.getType().getNullable() && row.getValue(f.getName()) == null) throw new IllegalArgumentException("null in non-nullable field " + f.getName()); }

boolean isRowEncodable(Row row, Schema schema) { return schema.getFields().stream().allMatch(f -> f.getType().getNullable() || row.getValue(f.getName()) != null); }

try { rowToProto(row); } catch (RuntimeException e) { if (e.getMessage().contains("Null value found")) { /* repair row or relax schema */ } else { throw e; } }

When it happens

Trigger: Calling rowToProto/fieldValueToProto (directly or via schema IO, e.g. ProtoSchema translation, schema-aware sinks) on a Row where a field declared non-nullable in the schema contains Java null.

Common situations: Row built with Row.withSchema missing values for some fields; mutation code that sets a field back to null; schema evolved to non-nullable after rows already contained nulls; mapping DB rows with NULL columns onto a non-nullable Beam schema.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• cannot encode a null Integer
• cannot encode a null Long
• cannot encode a null Short
• cannot encode a null BitSet
• cannot encode a null byte[]

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/e64317520509fd9a. Report an issue: GitHub.