[Flutter] When pressing the back button the application closes in flutter?

As the title says after pressing the back button, the application closes.

Container(
margin: EdgeInsets.only(left: 20, top: 8),
decoration: BoxDecoration(
color: colorYellow,
borderRadius: BorderRadius.all(Radius.circular(20))),
height: 40,
width: 40,
child: IconButton(
icon: Icon(Icons.arrow_back, color: Colors.white, size: 20),
onPressed: () => Navigator.of(context).pop(),
),
),

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