🐛 Fix issue that nodes did execute even if there was no input data

packages/core/src/WorkflowExecute.ts

@@ -401,6 +401,13 @@ export class WorkflowExecute {
 
 							nodeToAdd = parentNode;
 						}
+						const parentNodesNodeToAdd = workflow.getParentNodes(nodeToAdd as string);
+						if (parentNodesNodeToAdd.includes(parentNodeName) && nodeSuccessData[outputIndex].length === 0) {
+							// We do not add the node if there is no input data and the node that should be connected
+							// is a child of the parent node. Because else it would run a node even though it should be
+							// specifically not run, as it did not receive any data.
+							nodeToAdd = undefined;
+						}
 
 						if (nodeToAdd === undefined) {
 							// No node has to get added so process

packages/core/test/Helpers.ts

@@ -465,6 +465,30 @@ class NodeTypesClass implements INodeTypes {
 				},
 			},
 		},
+		'n8n-nodes-base.noOp': {
+			sourcePath: '',
+			type: {
+				description: {
+					displayName: 'No Operation, do nothing',
+					name: 'noOp',
+					icon: 'fa:arrow-right',
+					group: ['organization'],
+					version: 1,
+					description: 'No Operation',
+					defaults: {
+						name: 'NoOp',
+						color: '#b0b0b0',
+					},
+					inputs: ['main'],
+					outputs: ['main'],
+					properties: [],
+				},
+				execute(this: IExecuteFunctions): Promise<INodeExecutionData[][]> {
+					const items = this.getInputData();
+					return this.prepareOutputData(items);
+				},
+			},
+		},
 		'n8n-nodes-base.set': {
 			sourcePath: '',
 			type: {

packages/core/test/WorkflowExecute.test.ts

@@ -1154,6 +1154,174 @@ describe('WorkflowExecute', () => {
 					},
 				},
 			},
+			{
+				description: 'should not use empty data in sibling if parent did not send any data',
+				input: {
+					// Leave the workflowData in regular JSON to be able to easily
+					// copy it from/in the UI
+					workflowData: {
+						"nodes": [
+							{
+								"parameters": {},
+								"name": "Start",
+								"type": "n8n-nodes-base.start",
+								"typeVersion": 1,
+								"position": [
+									250,
+									300,
+								],
+							},
+							{
+								"parameters": {
+									"values": {
+										"number": [
+											{
+												"name": "value1",
+											},
+										],
+									},
+									"options": {},
+								},
+								"name": "Set",
+								"type": "n8n-nodes-base.set",
+								"typeVersion": 1,
+								"position": [
+									450,
+									300,
+								],
+							},
+							{
+								"parameters": {},
+								"name": "Merge",
+								"type": "n8n-nodes-base.merge",
+								"typeVersion": 1,
+								"position": [
+									1050,
+									250,
+								],
+							},
+							{
+								"parameters": {
+									"conditions": {
+										"number": [
+											{
+												"value1": "={{$json[\"value1\"]}}",
+												"operation": "equal",
+												"value2": 1,
+											},
+										],
+									},
+								},
+								"name": "IF",
+								"type": "n8n-nodes-base.if",
+								"typeVersion": 1,
+								"position": [
+									650,
+									300,
+								],
+							},
+							{
+								"parameters": {},
+								"name": "NoOpTrue",
+								"type": "n8n-nodes-base.noOp",
+								"typeVersion": 1,
+								"position": [
+									850,
+									150,
+								],
+							},
+							{
+								"parameters": {},
+								"name": "NoOpFalse",
+								"type": "n8n-nodes-base.noOp",
+								"typeVersion": 1,
+								"position": [
+									850,
+									400,
+								],
+							},
+						],
+						"connections": {
+							"Start": {
+								"main": [
+									[
+										{
+											"node": "Set",
+											"type": "main",
+											"index": 0,
+										},
+									],
+								],
+							},
+							"Set": {
+								"main": [
+									[
+										{
+											"node": "IF",
+											"type": "main",
+											"index": 0,
+										},
+									],
+								],
+							},
+							"IF": {
+								"main": [
+									[
+										{
+											"node": "NoOpTrue",
+											"type": "main",
+											"index": 0,
+										},
+										{
+											"node": "Merge",
+											"type": "main",
+											"index": 1,
+										},
+									],
+									[
+										{
+											"node": "NoOpFalse",
+											"type": "main",
+											"index": 0,
+										},
+									],
+								],
+							},
+							"NoOpTrue": {
+								"main": [
+									[
+										{
+											"node": "Merge",
+											"type": "main",
+											"index": 0,
+										},
+									],
+								],
+							},
+						},
+					},
+				},
+				output: {
+					nodeExecutionOrder: [
+						'Start',
+						'Set',
+						'IF',
+						'NoOpFalse',
+					],
+					nodeData: {
+						IF: [
+							[],
+						],
+						NoOpFalse: [
+							[
+								{
+									value1: 0,
+								},
+							],
+						],
+					},
+				},
+			},
 		];
 
 		const fakeLogger = {
@@ -1165,7 +1333,6 @@ describe('WorkflowExecute', () => {
 			error:  () => {},
 		} as ILogger;
 
-
 		const executionMode = 'manual';
 		const nodeTypes = Helpers.NodeTypes();
 		LoggerProxy.init(fakeLogger);
@@ -1213,7 +1380,6 @@ describe('WorkflowExecute', () => {
 				expect(result.finished).toEqual(true);
 				expect(result.data.executionData!.contextData).toEqual({});
 				expect(result.data.executionData!.nodeExecutionStack).toEqual([]);
-				expect(result.data.executionData!.waitingExecution).toEqual({});
 			});
 		}