[Fixed] Typeerror: error 1009: Cannot access properties or methods referenced by an empty object

1. Error description

TypeError: Error #1009: Cannot access properties or methods referenced by an empty object.
at FirstMap/search_clickHandler()[E:\Flash Builder\Map\src\FirstMap.mxml:17]
at FirstMap/__search_click()[E:\Flash Builder\Map\src\FirstMap.mxml:30]

2. Error reason

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
			   width="100%" height="100%" xmlns:chart="chart.*">

			import mx.controls.Alert;
			protected function search_clickHandler(event:MouseEvent):void
				var teacher:Teacher = new Teacher();
				var workId:String = teacher.workId.label;

		<!-- Place non-visual elements (e.g., services, value objects) here -->
	<mx:HBox width="100%" height="100%" paddingBottom="10" paddingLeft="10" paddingRight="20"
		<s:Panel width="50%" height="100%">
			<s:Button id="search" label="Check" click="search_clickHandler(event)" width="100%"
					  height="100%" fontSize="320"/>
		<chart:Teacher width="50%" height="100%"/>

Var workId: String = the teacher. The workId. Label; The label value of the workId in the Teacher module could not be obtained
Here the application calls parameters in the module

3. Solutions
(1) Check whether the label of the module workId is empty
(2) Debug the ActionScript code

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