postDebugTask-schema default value is ''

fixes #46675

src/vs/workbench/parts/debug/node/debugAdapter.ts

@@ -212,12 +212,12 @@ export class Adapter {
 			};
 			properties['preLaunchTask'] = {
 				type: ['string', 'null'],
-				default: null,
+				default: '',
 				description: nls.localize('debugPrelaunchTask', "Task to run before debug session starts.")
 			};
 			properties['postDebugTask'] = {
 				type: ['string', 'null'],
-				default: null,
+				default: '',
 				description: nls.localize('debugPostDebugTask', "Task to run after debug session ends.")
 			};
 			properties['internalConsoleOptions'] = INTERNAL_CONSOLE_OPTIONS_SCHEMA;