Error Codes

NPipeline error codes follow the pattern NPxxxx where the first two digits indicate the category.

NP01xx - Core Pipeline Errors

Code	Name	Description
NP0101	PipelineRequiresAtLeastOneNode	A pipeline must have at least one node. Add at least one source, transform, or sink.
NP0102	NodeMissingInputConnection	A non-source node has no input connection. Connect an upstream node to it.
NP0103	CyclicDependencyDetected	The pipeline graph contains a cycle. NPipeline requires a directed acyclic graph (DAG). The message names the nodes that could not be ordered and traces one cycle through them.
NP0104	NodeAlreadyAdded	A node with this ID has already been added to the builder. Use a unique ID.
NP0105	NodeNameNotUnique	A node with this name already exists. Choose a different name.

NP02xx - Type System Errors

Code	Name	Description
NP0201	TypeMismatchInConnection	Output type of the source node doesn't match input type of the target node.
NP0202	InputDataStreamWrongType	The input data stream is not of the expected type. Check node type parameters.
NP0203	CannotRegisterMappingsAfterExecution	Mapping registrations must happen before pipeline execution begins.
NP0204	RecordTypeHasNoPublicConstructor	The target record type has no public constructors. Add a public constructor.
NP0205	InvalidMemberAccessExpression	The member selector expression is invalid. Use a simple property accessor.
NP0206	MemberNotWritable	The target member is read-only. Use a writable property or constructor parameter.
NP0207	SetterCreationFailed	Failed to create a setter for the specified member via reflection.
NP0208	ValueTupleConstructorNotFound	Could not find the expected ValueTuple constructor.
NP0210	CannotConcatenateStreamsTypeMismatch	Cannot concatenate data streams of different types.
NP0211	NodeOutputTypeMismatch	A node produced items whose type does not match its declared output type, and no conversion applied.
NP0212	OutputAdaptationUnavailable	A node's output needs converting to its declared type but no converter exists for that node kind.
NP0213	InputStreamContractMismatch	A node received input items of a type it cannot consume. Check the connection's source node.
NP0214	RouteNodeMissingOutputType	A route node has no output item type. Add it with PipelineBuilder.AddRoute<T>(), or set OutputType on a custom route definition.

NP03xx - Node Execution Errors

Code	Name	Description
NP0301	NodeKindNotSupported	The node kind is not supported or its execution delegate was not bound.
NP0302	OutputNotFoundForSourceNode	Could not locate the output data stream for a source node.
NP0303	PipelineExecutionFailedAtNode	Execution failed at a specific node. Check the NodeId in the exception.
NP0304	PipelineExecutionFailed	The pipeline execution failed. Check the inner exception for details.
NP0305	Retired	Never raised. An item that runs out of retries raises NP0311. Not reused.
NP0306	Retired	Never raised. A resilience policy that throws fails the node with its own exception. Not reused.
NP0307	LineageCardinalityMismatch	The number of lineage inputs doesn't match the number of outputs. Internal framework error.
NP0308	FailedToExtractItemsFromInMemoryDataStream	Could not extract items from an InMemoryDataStream. Internal framework error.
NP0310	Retired	No longer used. It belonged to CircuitBreakerTrippedException, which was never thrown and has been removed. An open breaker raises CircuitBreakerOpenException.
NP0311	RetryLimitExhausted	RetryExhaustedException: an item, a node retry, or a node restart ran out of attempts. AttemptCount is the number of attempts, and the inner exception is the last failure.

NP04xx - Configuration and Setup Errors

Code	Name	Description
NP0401	ExecutionStrategyCannotBeSetForNonTransformNode	Execution strategies can only be applied to transform nodes.
NP0402	NodeNotFoundInBuilder	The referenced node was not found in the pipeline builder.
NP0403	Retired	Belonged to WithResilience(NodeHandle), which node restart options replaced. Not reused.
NP0404	InvalidErrorHandlerType	The error handler type doesn't implement the required interface.
NP0405	PreConfiguredInstanceAlreadyAdded	A pre-configured instance for this node has already been registered.
NP0406	PreConfiguredInstanceNodeNotFound	The node for the pre-configured instance was not found in the builder.
NP0407	MergeStrategyNotSupported	The specified merge strategy is not supported.
NP0408	NodeActivationFailed	Could not instantiate the node type. Check constructors and DI registrations.
NP0411	JoinNodeRequiresTwoKeySelectorAttributes	Join nodes require exactly two [KeySelector] attribute declarations.
NP0412	UnbatchingNodeNotSupported	UnbatchingNode cannot be executed directly; use the unbatching execution strategy.
NP0413	BatchingNodeNotSupported	BatchingNode doesn't support per-item transformation; use the batching execution strategy.
NP0414	CustomMergeNodeMissingInterface	The custom merge node is missing the required interface implementation.
NP0415	Retired	Never raised. A dead-lettered item with no dead-letter sink raises NP0424. Not reused.
NP0416	LineageAdapterMissing	Internal: lineage adapter not configured.
NP0417	SourceNodeLineageUnwrapMissing	Internal: source node lineage unwrap delegate not configured.
NP0418	SinkNodeLineageUnwrapMissing	Internal: sink node lineage unwrap delegate not configured.
NP0419	MissingTypeMetadata	Internal: node is missing type metadata.
NP0420	TimeWindowAssignerCannotBeNull	The time window assigner cannot be null for time-windowed operations.
NP0421	StreamTransformNodeRequiresStreamStrategy	A stream transform node was configured with a strategy that cannot execute streams.
NP0422	NodeCannotSupplyExecutionStrategy	A node scheduled as a transform does not implement the transform interface.
NP0423	NodeIdNotResolvable	A node asked the context for its own id, and no single id matched. Either no pipeline run owns the context (the node is being called directly, as in a unit test), or the same instance is wired into the graph under more than one id. Use TryGetNodeId where a node can run outside a pipeline, or give each graph position its own instance.
NP0424	DeadLetterSinkNotConfigured	An item was dead-lettered, but the pipeline has no dead-letter sink. A transform with OnItemFailure = ItemFailureAction.DeadLetter raises it before any node starts; a custom resilience policy that returns DeadLetter raises it when the item fails. Add a sink with AddDeadLetterSink, or use Skip or Fail.
NP0425	NodeRestartRequiresResumableStrategy	A transform has NodeRestart.MaxRestarts above zero, but its execution strategy does not implement IResumableExecutionStrategy. Use a resumable strategy, or set MaxRestarts to 0 for that node.
NP0426	DuplicateJoinKey	A one-to-one keyed join dead-letters an item because its key was a duplicate: the key had already matched, or the same input already had an item waiting for it. The join does not fail; the item goes to the dead-letter sink as a DuplicateJoinKeyException. Use Drop or EmitAsUnmatched if duplicates are expected.
NP0427	JoinOptionsRequireOneToOne	A keyed join sets DuplicateKeyPolicy or MaxMatchedKeys, which apply only to one-to-one joins, while Cardinality is ManyToMany. Set Cardinality = JoinCardinality.OneToOne, or remove the options.

NP05xx - Resource Management Errors

Code	Name	Description
NP0501	ContextDisposalFailed	One or more errors occurred while disposing pipeline context resources.
NP0502	DeadLetterQueueCapacityExceeded	BoundedInMemoryDeadLetterSink is full, and it throws InvalidOperationException instead of growing. Raise its capacity, or use a sink that writes somewhere durable.
NP0503	Retired	Belonged to the node restart materialization buffer, which the replay window replaced. NodeRestart.MaxReplayWindow applies backpressure instead of failing. Not reused.
NP0504	BatchSizeMustBeGreaterThanZero	Batch size must be a positive integer.

Next Steps

• Build-Time Analyzers - build-time diagnostic rules
• Common Issues - symptom-based troubleshooting