Datepicker and get the Date Variable. Help

[alevi12]

Code 1:

<?php
$path2shared = "../../00_Shared/";
include_once($path2shared."common_includes.php");
include_once($path2shared."/jasper/jasperserver/JasperReportPDF.php");

$Start_Datum  = $_GET['Start_Datum'];                                              //  NULL
$Ende_Datum         = $_GET['Ende_Datum'];

If (empty($Start_Datum)){
$Start_Datum = new DateTime("01.01.1990") ;
}

If (empty($Ende_Datum)){
$Ende_Datum = new DateTime("31.12.2030");
}

if (empty($LOCALE)){
 $LOCALE = JasperReportLocales::REPORT_LOCALE_DEFAULT;
}

$report_params = array( 'Start_Datum'=>sprintf('%s',$Start_Datum->format("U")*1000), 
                                         'Ende_Datum'=>sprintf('%s',$Ende_Datum->format("U")*1000),

 

Code 2:

class ReportSelectorWriter
{
 public static function writeHTML($selector,$locale_selector=null){
  $log = $selector->getLogger();
  
  $form_name = "form_".$selector->getName();
  
  jquery_add_datepicker($form_name."_datepicker_start");
  jquery_add_datepicker($form_name."_datepicker_end");

echo("      Start  <input name="".$Start_Datum."" id="".$form_name."_datepicker_start" type="text" size="10" maxlength="10" onChange="suchzeitraum_check(document".$form_name."_datepicker_start,document".$form_name."_datepicker_end)">n");

 echo("Ende  <input name="Ende_Datum" id="".$form_name."_datepicker_end" type="text" size="10" maxlength="10" onChange="suchzeitraum_check(document".$form_name."_datepicker_start,document".$form_name."_datepicker_end);">n");

 

Now I want that when the date in the field is empty, then he should accept the date which I had previously already defined in Code 1.
When I click on the button to create a report and in this report, the respective date will then be created which is in the field of DatePicker and when is empty, it should take the date that I've already defined.

The variable $Start_Datum and $Ende_Datum were created in iReport.

For advice and help, I would be very grateful. Thank you