I dont understand what is happening here? any suggestions? This is happening on this line :-

var explode = gregorianDate.split('-');

Here is full function.

function updateCalendarDay(){ 

    if (document.getElementById('gregorianDateOutput') != null) {

       var gregorianDate = document.getElementById('gregorianDateOutput').value;

    }else{

       var gregorianDate = null;

    }

    if(gregorianDate != ){

       var explode = gregorianDate.split('-');

       var year = explode[0];

       var month = explode[1];

       var day = explode[2];

       document.getElementById('month').value = month;

       document.getElementById('year').value = year;

       var ajax = new GLM.AJAX();

       var url='calendarAjax.php?month='+month+'&year='+year+'&day='+day;

       ajax.callPage(url, showSubscribeResult, GET);

    }           

}