void main() {

// This is a String var userName = 'Bob'; print('value of userName is: ' + userName); // Bob

// reset 1 userName = ''; // ok print('value of userName is: ' + userName); // empty string print(userName.runtimeType); // String

// reset 2 -> noz OK, becase userName holds a String value // userName = null;

String? theSolution = 'This is the solution'; print('value of theSolution is: ' + theSolution); // 'This is the solution'

// now set to null is working, because of String? theSolution = null; print(theSolution); print(theSolution.runtimeType); }