fix: Load workflows with unconnected Switch outputs (#12020)

packages/core/src/PartialExecutionUtils/DirectedGraph.ts

@@ -448,7 +448,7 @@ export class DirectedGraph {
 
 			for (const [outputType, outputs] of Object.entries(iConnection)) {
 				for (const [outputIndex, conns] of outputs.entries()) {
-					for (const conn of conns) {
+					for (const conn of conns ?? []) {
 						// TODO: What's with the input type?
 						const { node: toNodeName, type: _inputType, index: inputIndex } = conn;
 						const to = workflow.getNode(toNodeName);

packages/core/src/PartialExecutionUtils/__tests__/DirectedGraph.test.ts

@@ -42,6 +42,28 @@ describe('DirectedGraph', () => {
 		);
 	});
 
+	//    ┌─────┐    ┌─────┐──► null
+	//    │node1├───►│node2|   ┌─────┐
+	//    └─────┘    └─────┘──►│node3|
+	//                         └─────┘
+	//
+	test('linear workflow with null connections', () => {
+		// ARRANGE
+		const node1 = createNodeData({ name: 'Node1' });
+		const node2 = createNodeData({ name: 'Node2' });
+		const node3 = createNodeData({ name: 'Node3' });
+
+		// ACT
+		const graph = new DirectedGraph()
+			.addNodes(node1, node2, node3)
+			.addConnections({ from: node1, to: node2 }, { from: node2, to: node3, outputIndex: 1 });
+
+		// ASSERT
+		expect(DirectedGraph.fromWorkflow(graph.toWorkflow({ ...defaultWorkflowParameter }))).toEqual(
+			graph,
+		);
+	});
+
 	describe('getChildren', () => {
 		// ┌─────┐    ┌─────┐   ┌─────┐
 		// │node1├───►│node2├──►│node3│

packages/core/src/WorkflowExecute.ts

@@ -36,6 +36,7 @@ import type {
 	CloseFunction,
 	StartNodeData,
 	NodeExecutionHint,
+	NodeInputConnections,
 } from 'n8n-workflow';
 import {
 	LoggerProxy as Logger,
@@ -208,6 +209,9 @@ export class WorkflowExecute {
 				// Get the data of the incoming connections
 				incomingSourceData = { main: [] };
 				for (const connections of incomingNodeConnections.main) {
+					if (!connections) {
+						continue;
+					}
 					for (let inputIndex = 0; inputIndex < connections.length; inputIndex++) {
 						connection = connections[inputIndex];
 
@@ -249,6 +253,9 @@ export class WorkflowExecute {
 				incomingNodeConnections = workflow.connectionsByDestinationNode[destinationNode];
 				if (incomingNodeConnections !== undefined) {
 					for (const connections of incomingNodeConnections.main) {
+						if (!connections) {
+							continue;
+						}
 						for (let inputIndex = 0; inputIndex < connections.length; inputIndex++) {
 							connection = connections[inputIndex];
 
@@ -642,7 +649,7 @@ export class WorkflowExecute {
 					}
 					for (const connectionDataCheck of workflow.connectionsBySourceNode[parentNodeName].main[
 						outputIndexParent
-					]) {
+					] ?? []) {
 						checkOutputNodes.push(connectionDataCheck.node);
 					}
 				}
@@ -661,7 +668,7 @@ export class WorkflowExecute {
 				) {
 					for (const inputData of workflow.connectionsByDestinationNode[connectionData.node].main[
 						inputIndex
-					]) {
+					] ?? []) {
 						if (inputData.node === parentNodeName) {
 							// Is the node we come from so its data will be available for sure
 							continue;
@@ -681,7 +688,7 @@ export class WorkflowExecute {
 							if (
 								!this.incomingConnectionIsEmpty(
 									this.runExecutionData.resultData.runData,
-									workflow.connectionsByDestinationNode[inputData.node].main[0],
+									workflow.connectionsByDestinationNode[inputData.node].main[0] ?? [],
 									runIndex,
 								)
 							) {
@@ -770,7 +777,7 @@ export class WorkflowExecute {
 						} else if (
 							this.incomingConnectionIsEmpty(
 								this.runExecutionData.resultData.runData,
-								workflow.connectionsByDestinationNode[nodeToAdd].main[0],
+								workflow.connectionsByDestinationNode[nodeToAdd].main[0] ?? [],
 								runIndex,
 							)
 						) {
@@ -1066,7 +1073,7 @@ export class WorkflowExecute {
 					if (workflow.connectionsByDestinationNode.hasOwnProperty(executionNode.name)) {
 						// Check if the node has incoming connections
 						if (workflow.connectionsByDestinationNode[executionNode.name].hasOwnProperty('main')) {
-							let inputConnections: IConnection[][];
+							let inputConnections: NodeInputConnections;
 							let connectionIndex: number;
 
 							// eslint-disable-next-line prefer-const
@@ -1586,7 +1593,7 @@ export class WorkflowExecute {
 								// Iterate over all the different connections of this output
 								for (connectionData of workflow.connectionsBySourceNode[executionNode.name].main[
 									outputIndex
-								]) {
+								] ?? []) {
 									if (!workflow.nodes.hasOwnProperty(connectionData.node)) {
 										throw new ApplicationError('Destination node not found', {
 											extra: {