fix(Notion Node): Handle empty values correctly for Notion selects + multi selects (#7383)

Github issue / Community forum post (link here to close automatically):

packages/nodes-base/nodes/Notion/GenericFunctions.ts

@@ -320,6 +320,10 @@ function getDateFormat(includeTime: boolean) {
 	return '';
 }
 
+function isEmpty(value: unknown): boolean {
+	return value === undefined || value === null || value === '';
+}
+
 function getPropertyKeyValue(
 	this: IExecuteFunctions,
 	value: any,
@@ -368,7 +372,16 @@ function getPropertyKeyValue(
 			};
 			break;
 		case 'multi_select':
+			if (isEmpty(value.multiSelectValue)) {
+				result = {
+					type: 'multi_select',
+					multi_select: [],
+				};
+				break;
+			}
+
 			const multiSelectValue = value.multiSelectValue;
+
 			result = {
 				type: 'multi_select',
 				multi_select: (Array.isArray(multiSelectValue)
@@ -403,6 +416,14 @@ function getPropertyKeyValue(
 			};
 			break;
 		case 'select':
+			if (isEmpty(value.selectValue)) {
+				result = {
+					type: 'select',
+					select: null,
+				};
+				break;
+			}
+
 			result = {
 				type: 'select',
 				select: version === 1 ? { id: value.selectValue } : { name: value.selectValue },