求教一个JQuery源码的有关问题，请指点上

var jQuery = function( selector, context ) {
        return new jQuery.fn.init( selector, context );
    };
    jQuery.fn = jQuery.prototype = {
        init: function( selector, context ) {
            var match, elem, ret, doc;

            // Handle $(""), $(null), or $(undefined)
            if ( !selector ) {
                return this;
            }
        }
    };
console.log(jQuery(null));