{"record":{"id":"460923ba183aa41b","repo":"apache/flink","slug":"field-fieldidx-is-null-but-expected-to-hold-a-v","errorCode":null,"errorMessage":"Field {fieldIdx} is null, but expected to hold a value.","messagePattern":"Field (.+?) is null, but expected to hold a value\\.","errorType":"exception","errorClass":"NullFieldException","httpStatus":null,"severity":"error","filePath":"flink-core/src/main/java/org/apache/flink/api/java/typeutils/runtime/TupleSerializer.java","lineNumber":141,"sourceCode":"            return null;\n        }\n\n        for (int i = 0; i < arity; i++) {\n            Object copy = fieldSerializers[i].copy((Object) from.getField(i), reuse.getField(i));\n            reuse.setField(copy, i);\n        }\n\n        return reuse;\n    }\n\n    @Override\n    public void serialize(T value, DataOutputView target) throws IOException {\n        for (int i = 0; i < arity; i++) {\n            Object o = value.getField(i);\n            try {\n                fieldSerializers[i].serialize(o, target);\n            } catch (NullPointerException npex) {\n                throw new NullFieldException(i, npex);\n            }\n        }\n    }\n\n    @Override\n    public T deserialize(DataInputView source) throws IOException {\n        T tuple = instantiateRaw();\n        for (int i = 0; i < arity; i++) {\n            Object field = fieldSerializers[i].deserialize(source);\n            tuple.setField(field, i);\n        }\n        return tuple;\n    }\n\n    @Override\n    public T deserialize(T reuse, DataInputView source) throws IOException {\n        for (int i = 0; i < arity; i++) {\n            Object field = fieldSerializers[i].deserialize(reuse.getField(i), source);","sourceCodeStart":123,"sourceCodeEnd":159,"githubUrl":"https://github.com/apache/flink/blob/2f3c205e9266cb30240eb7f4fdab15cad629a70f/flink-core/src/main/java/org/apache/flink/api/java/typeutils/runtime/TupleSerializer.java#L123-L159","documentation":"TupleSerializer.serialize writes each tuple field with its field serializer. When a field's value is null and the field serializer throws NullPointerException from serialize, it is converted into NullFieldException(i) with message 'Field {fieldIdx} is null, but expected to hold a value.' Standard Flink tuple serializers do not support null fields (only tuple fields of type-nullable wrappers handled by specific serializers); a null field value therefore aborts serialization of the whole record.","triggerScenarios":"Serializing a tuple (network shuffle, checkpointing, writing to a sink) where value.getField(i) is null for a primitive-typed field serializer (e.g. StringValue, LongValue-based serializers) whose serialize(null) NPEs -> NullFieldException(i) naming the field index.","commonSituations":"Source data with missing/optional attributes mapped into tuple fields using Value-type serializers (StringValue etc.) instead of null-tolerant ones (String field via StringSerializer handles null differently; Value types never do). Left-join or enrichment steps producing nulls. Reusing a TupleX of Value objects where some elements were left null by constructor defaults.","solutions":["Replace nulls with type-appropriate defaults (empty StringValue, 0L) before serialization, or filter incomplete records.","If nulls must be represented, use plain Java wrapper types (String, Long) with Flink's standard TypeInfo so nullability is encoded, or use a custom TypeInformation whose serializers handle nulls (e.g. SqlTimestamp/nullable wrappers).","Identify the offending field from the NullFieldException field index and fix that specific upstream producer."],"exampleFix":"// before\nTuple2<StringValue, LongValue> t = Tuple2.of(null, new LongValue(1));\n// serializer.serialize(t, out) -> NullFieldException(0)\n\n// after\nTuple2<StringValue, LongValue> t = Tuple2.of(new StringValue(\"\"), new LongValue(1));\nserializer.serialize(t, out);","handlingStrategy":"validation","validationCode":"public static boolean allFieldsNonNull(Tuple t) {\n    for (int i = 0; i < t.getArity(); i++) {\n        if (t.getField(i) == null) return false;\n    }\n    return true;\n}\n// stream.filter(RecordUtil::allFieldsNonNull) or default-fill before serialize","typeGuard":"public static boolean tupleSerializableSafe(Tuple2<String,Long> t) {\n    return t.f0 != null && t.f1 != null;\n}","tryCatchPattern":"try {\n    serializer.serialize(value, out);\n} catch (org.apache.flink.api.java.typeutils.runtime.NullFieldException e) {\n    // e.getFieldIndex() names the null field; fix that producer or default-fill it\n}","preventionTips":["Default-fill or filter null tuple fields before serialization/shuffle/checkpoint.","Use nullable-capable types (String, boxed types) with matching serializers rather than Value types for optional fields.","Log the field index from NullFieldException to pinpoint the offending producer quickly."],"tags":["tuple","null-field","serialization","data-quality","typeutils"],"backgroundTag":null,"analyzedSha":"2f3c205e9266cb30240eb7f4fdab15cad629a70f","analyzedAt":"2026-08-14T08:48:24.518Z","schemaVersion":2},"datasetVersion":"2026-08-14T10:17:34.591Z"}