Original subtitles

There is an important value built into Dart which we hadn't had a look at yet.

We had a look at string values between the quotes, at integers, doubles and so on

but what we hadn't had a look at yet is the null value.

Null simply is a value built into Dart which you can use if you might generally expect another type of

value,

let's say you have a username and that is Max

but then something in your application happens and you want to reset that to an uninitialized state

so to say and in such cases, you can set this to null.

This does not violate the rule or the inference of username being a string,

so just to prove this, if I would assign a number here, then actually here I would get an error because

a number is of course not a string, an integer is not a string.

Null is assignable here even though it's of course not wrapped between quotes,

null can basically be assigned to any type,

so no matter if you normally expect a string, integer, double, whatever it is, null can always be assigned

and you often assign it to reset a variable, to reset the value in a variable, to indicate that you have no

value yet, anything like that.

You can also use it in boolean comparisons.

So if you have an if check and you want to find out if username is set, you could check if username

is not equal to null for example. That would be something where you would also use null because right

now if I don't assign a value, this would for example be null, the default uninitialized state is that

this is null

so then such a check here could be useful.

So using null to reset values or in checks to make sure that you have a value and you're not in an uninitialized

state can be very important and Dart will use it throughout this course and therefore null is a value you should

be aware of.