What causes "Null value set on non-nullable field " in apache/beam?

Make the field nullable in the schema (FieldType.withNullable(true)) or in the POJO annotation

apache/beam · error · java.lang.RuntimeException

Null value set on non-nullable field <field>

Error message

Null value set on non-nullable field <field>

What it means

RowWithGetters.getValue checks that a field accessed through its getters is not null when the schema declares the field non-nullable. A null was stored (via a getter) in a field declared non-nullable, so reading it throws RuntimeException. This is a data-integrity check for the row's declared schema.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/values/RowWithGetters.java:93

        cache = new TreeMap<>();
      }
      fieldValue =
          cache.computeIfAbsent(
              fieldIdx,
              new Function<Integer, @Nullable Object>() {
                @Override
                public @Nullable Object apply(Integer idx) {
                  FieldValueGetter<T, Object> getter = getters.get(idx);
                  checkStateNotNull(getter);
                  return getter.get(getterTarget);
                }
              });
    } else {
      fieldValue = getters.get(fieldIdx).get(getterTarget);
    }

    if (fieldValue == null && !field.getType().getNullable()) {
      throw new RuntimeException("Null value set on non-nullable field " + field);
    }
    return (W) fieldValue;
  }

  public TypeDescriptor<?> getGetterTargetType() {
    return getterTargetType;
  }

  private boolean cacheFieldType(Field field) {
    TypeName typeName = field.getType().getTypeName();
    return typeName.equals(TypeName.MAP)
        || typeName.equals(TypeName.ARRAY)
        || typeName.equals(TypeName.ITERABLE);
  }

  @Override
  public int getFieldCount() {
    return getters.size();

View on GitHub (pinned to 12126d8942)

Solutions

Make the field nullable in the schema (FieldType.withNullable(true)) or in the POJO annotation
Ensure the backing object's field is populated before wrapping it in a Row (set defaults in the constructor)
Rebuild/validate the row after mutations; use Schema validation on creation instead of trusting lazy getters

Example fix

// before
class User { String id; } // id left null, schema non-nullable
// after
class User { String id = "unknown"; } // or mark field nullable in schema

Defensive patterns

Strategy: try-catch

Validate before calling

schema.getFields().forEach(f -> { if (!f.getType().getNullable() && backing.get(f.getName()) == null) throw new IllegalStateException("null in non-nullable field " + f.getName()); });

Type guard

boolean isReadable(Row row, int idx) { return idx >= 0 && idx < row.getSchema().getFieldCount(); }

Try / catch

try { W v = row.getValue(idx); } catch (RuntimeException e) { if (e.getMessage().startsWith("Null value set on non-nullable field")) { /* handle null per schema */ } else throw e; }

Prevention

Initialize all non-nullable POJO fields with defaults
Avoid mutating backing objects after wrapping in a Row
Align @DefaultSchema annotations with runtime nullability

When it happens

Trigger: Calling row.getValue(idx)/accessors on a RowWithGetters whose underlying getter target object has null in a field whose Schema.FieldType.getNullable() is false; typically the row was built without validation or the backing object mutated after creation.

Common situations: POJOs annotated with @DefaultSchema where fields are null but the generated schema marks them non-nullable; mutation of the backing object after row creation; schema/POJO divergence after refactoring.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/9544ce9f9f222e19. Report an issue: GitHub.