Apex class behavior with Null instance of Sobject

Apex_Sobject_member_to_null.cls

/*
 	MyController cnt = new MyController();
	cnt.tst.Name = 'test';
	cnt.tst = null;
	system.debug('Test outside: '+(cnt.tst.Name == null));	//Test outside: true
	system.debug('Test outside: '+(cnt.tst == null));	//Test outside: true
	system.debug('Test outside: '+json.serializepretty(cnt.tst)); //Test outside: null
	cnt.myMethod(); //Throws null pointer exceptions
 */
public class MyController {
    public Account tst{get;set;}
    public MyController(){
        this.tst = [Select Id, Name From Account limit 1];
    }
    
    public void myMethod(){
        system.debug('Test inside: '+(tst.Name == null)); //Throws null pointer exceptions
        system.debug('Test inside: '+(tst == null));
        system.debug('Test inside: '+json.serializepretty(tst));
    }
}

@logontokartik in this context this.tst and tst refers to the same inner member, there are no other "tst" variables, how did you explain this regarding the Apex engine?