{"record":{"id":"253e8457fc0f32e7","repo":"nautechsystems/nautilus_trader","slug":"chunk-must-have-at-least-one-element-to-encode-253e84","errorCode":null,"errorMessage":"Chunk must have at least one element to encode","messagePattern":"Chunk must have at least one element to encode","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"crates/serialization/src/arrow/mod.rs","lineNumber":314,"sourceCode":"        data: &[Self],\n    ) -> Result<RecordBatch, ArrowError>;\n\n    /// Returns the metadata for this data element.\n    fn metadata(&self) -> HashMap<String, String>;\n\n    /// Returns the metadata selected for a chunk.\n    ///\n    /// The default uses the first element. Implementations may override this when leading sentinel\n    /// values do not carry meaningful metadata.\n    ///\n    /// # Panics\n    ///\n    /// Panics if `chunk` is empty.\n    fn chunk_metadata(chunk: &[Self]) -> HashMap<String, String> {\n        chunk\n            .first()\n            .map(Self::metadata)\n            .expect(\"Chunk must have at least one element to encode\")\n    }\n}\n\n/// Decodes data types from Apache Arrow RecordBatch format.\npub trait DecodeFromRecordBatch\nwhere\n    Self: Sized + Into<Data> + ArrowSchemaProvider,\n{\n    /// Decodes a `RecordBatch` into a vector of values of the implementing type, using the provided metadata.\n    ///\n    /// # Errors\n    ///\n    /// Returns an `EncodingError` if the decoding fails.\n    fn decode_batch(\n        metadata: &HashMap<String, String>,\n        record_batch: RecordBatch,\n    ) -> Result<Vec<Self>, EncodingError>;\n}","sourceCodeStart":296,"sourceCodeEnd":332,"githubUrl":"https://github.com/nautechsystems/nautilus_trader/blob/18893faf8b356be3320add8de2f861b0b647cf06/crates/serialization/src/arrow/mod.rs#L296-L332","documentation":"The default EncodeToRecordBatch::chunk_metadata takes metadata from the chunk's first element; an empty slice has none, so the documented panic fires. Metadata (e.g. instrument/venue info) must come from at least one item.","triggerScenarios":"Calling chunk_metadata (or the encoder that uses it) with an empty &[Self] — e.g. encode_chunk on a zero-length data slice for any Arrow-encodable type.","commonSituations":"Flush loops that call the encoder unconditionally per buffer even when nothing accumulated; filtered datasets yielding no rows for a time range.","solutions":["Check chunk.is_empty() before encoding and skip the write.","Restructure the writer to only invoke the encoder on non-empty batches.","If an empty RecordBatch must be written, use the schema directly rather than deriving metadata from items."],"exampleFix":"// before\nlet metadata = T::chunk_metadata(&chunk);\n// after\nassert!(!chunk.is_empty(), \"skipped encode: empty chunk\");\nif chunk.is_empty() { return; }\nlet metadata = T::chunk_metadata(&chunk);","handlingStrategy":"validation","validationCode":"if chunk.is_empty() { return; } // skip encode","typeGuard":"fn has_items<T>(chunk: &[T]) -> bool { !chunk.is_empty() }","tryCatchPattern":"let result = std::panic::catch_unwind(|| T::chunk_metadata(&chunk));","preventionTips":["Guard every encode_chunk call site with an emptiness check","Only invoke the Arrow encoder on non-empty batches","Use schema-only writes when an empty batch must be produced"],"tags":["rust","serialization","arrow","empty-collection"],"backgroundTag":"empty-required-field","analyzedSha":"18893faf8b356be3320add8de2f861b0b647cf06","analyzedAt":"2026-09-08T20:49:34.690Z","contentChangedAt":"2026-09-08T20:49:34.690Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}