Annotation for Google Compiler, @type function with optional parameter

Question

I have searched the google to it's last page and haven't found an answer for this.

How do i annotate a function in the scope of another object which can take as parameters either a string, an array of strings or no parameter at all ?

I tried this:

/**
 * @type function(this:anObject, (string|Array.<string>)=)
 */
deselect = function(val) {
    var temp = val ? ( val instanceof Array ? val : [val]) : [];
    // some code
    this.doSomething(temp);
}.bind(anObject);

But it doesn't work because when i call it without a parameter, the compiler gives back an error like this:

WARNING - assignment
    found   : function (?): undefined
    required: function (this:anObject, (Array.<string>|null|string)=): ?
        deselect = function(val) {

Answer 1

I tend to hate the type checking that Google Closure Compiler works with.

To answer my own question:

To pass the assignment check form the bind return you have to recast the new function as follows:

/**
 * @type function(this:anObject, (string|Array.<string>)=)
 */
deselect = /** @type function(this:anObject, (string|Array.<string>)=) */
(function(val) {
    var temp = val ? ( val instanceof Array ? val : [val]) : [];
    // some code
    this.doSomething(temp);
}.bind(anObject));

If anyone has any idea of how to make this less creepy as it already is, please post it here.