Learning Null Check Operator

Boo.cs

public class Boo
{

}

Foo.cs

public class Foo
{
    public Boo Boo { get; set; }
    public List<Boo> BooList { get; set; }
}

LearningNullCheckOperator .cs

Foo fooWithBoo = new Foo()
{
    Boo = new Boo()
};

Foo fooWithNullBoo = new Foo()
{
    Boo = null
};

Foo nullFoo = null;


Console.WriteLine($"booIsNotNull1 = fooWithBoo?.Boo != null;     -> { fooWithBoo?.Boo != null }");          // True
Console.WriteLine($"booIsNotNull2 = fooWithNullBoo?.Boo != null; -> { fooWithNullBoo?.Boo != null }");      // False
Console.WriteLine($"booIsNotNull3 = nullFoo?.Boo != null;        -> { nullFoo?.Boo != null }");             // False
Console.WriteLine($"booIsNull = nullFoo?.Boo == null;            -> { nullFoo?.Boo == null }");             // True


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
    
Foo fooWithBooList = new Foo()
{
    BooList = new List<Boo>()
    {
        new Boo(),
        new Boo(),
        new Boo()
    }
};

Foo fooWithoutBooList = new Foo()
{
    BooList = null
};

Console.WriteLine($"fooWithBooList?.BooList.Count > 0      -> { fooWithBooList?.BooList?.Count > 0 }");      // True
Console.WriteLine($"fooWithoutBooList?.BooList.Count > 0   -> { fooWithoutBooList?.BooList?.Count > 0 }");   // False
Console.WriteLine($"fooNull?.BooList.Count > 0             -> { fooNull?.BooList?.Count > 0 }");             // False