"Non-nullable field 'X' is uninitialized" Warning.

Hi Nimrod m, thank you for your question.

This warning comes from the compiler, that's why Rider shows it. Showing this warning is useful when "warnings as errors" is enabled. Otherwise, the project will not compile, and there will be no explanation in the editor.

In addition, the compiler does not know what code is written in the MyString setter.

You can workaround the problem by annotating the setter to let the compiler know that the setter should initialize the field. The compiler uses this information in the constructor to know that the field has been initialized and, when parsing the setter, checks that the annotation is correct.

#nullable enable
        public class MyClass
    {
        private string myString;

        public MyClass()
        {
            myString = "";
        }

        public MyClass(string myString)
        {
            MyString = myString;
        }

        public string MyString
        {
            get => myString;
            [System.Diagnostics.CodeAnalysis.MemberNotNull("myString")]
            set
            {
                myString = value;
            }
        }
    }

 private string? myString;