[Flutter] Private variables giving the warning not in use try removing the variable

I recently started learning Dart and come accross this warning in Dart pad. I don't why this warning is thrown. Can any body explain what is going on here. I have attaced the screenshot.enter image description here

I didn't expected the warning as the _name variable is in use in the constructer for setting tbe value.

Code:

void main() {
final ani = Animal('Tiger', 23);
ani.setName = 'Tiggerr';
}

class Animal {
String _name;
final int age;

Animal(this._name, this.age) {
print('hello from constructer');
}

set setName(String newName){
_name = newName;
}
}

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