I have two warning and i don't understand why ...

Why i get these weak warnings?

let test = function()
{
    /** @type {string|null} */
    this.One = null; // Assigned expression type null is not assignable to type string.
    /** @type {string|null} */
    let Two = null; // But this works without warning and is the same.

    // Why the first object is no checking for the 'null' if i defined in type?
    // If i disable the 'Type mismatch' will stop the 'Two' for validating correctly if i put a number.


    this.Call = () =>
    {
        // Condition is always false since types 'string' and 'null' have no overlap
        // I don't understand this message why 'Is always false'. If is 'null === null' is true.
        // Why this message is shows from the first place?

        // In 'Inspection Results' its say: Comparison of expressions having incompatible types. What?
        // That is the point of '===' to checking if the variables is equal and the same type.
        // I already say on '@type' can be 'null', Why is incompatible types?

        if (Two === null) {}
    }
};

If i have like this:

let test2 = function()
{
    /** @type {String} */
    this.One = null; // No warnings.
    /** @type {String} */
    let Two = null; // No warnings.

    this.Call = () =>
    {
        // No warnings.

        if (Two === null) {}
    }
};