#25 - empty Date/DateTime means empty string not null.

Thanks to @thomasdv for bugreport!

Author: Vitexus

Examples/UpdateInvoice.php

@@ -0,0 +1,27 @@
+#!/usr/bin/php -f
+<?php
+
+/**
+ * AbraFlexi - Example how to create Invoice
+ *
+ * @author     Vítězslav Dvořák <[email protected]>
+ * @copyright  (G) 2018 Vitex Software
+ */
+
+namespace Example\AbraFlexi;
+
+use \AbraFlexi\RO;
+use \AbraFlexi\FakturaVydana;
+
+define('EASE_LOGGER', 'syslog|console');
+include_once './config.php';
+include_once '../vendor/autoload.php';
+
+$invoiceId = 1;
+
+$inv = new FakturaVydana($invoiceId);
+$inv->takeData(["stavMailK" => "stavMail.odeslano"]);
+$inv->sync();
+
+$inv->addStatusMessage(_('Invoice') . ': ' . $inv->getRecordIdent() . ' ' . $inv->getRecordCode(),
+        $inv->sync() ? 'success' : 'error' );

src/AbraFlexi/Date.php

@@ -51,7 +51,7 @@ public function __construct(string $flexidate = 'NOW') {
      * @return string
      */
     public function __toString() {
-        return $this->isNull ? null : $this->format(RO::$DateFormat);
+        return $this->isNull ? '' : $this->format(RO::$DateFormat);
     }
 
 }

src/AbraFlexi/DateTime.php

@@ -34,7 +34,7 @@ public function __construct(string $flexidatetime = 'NOW') {
         $format = '';
         if (strchr($flexidatetime, '.')) { //NewFormat
             $format = RO::$DateTimeFormat;
-        } elseif ( !empty ($flexidatetime) && ($flexidatetime != 'NOW')) { // Old format
+        } elseif (!empty($flexidatetime) && ($flexidatetime != 'NOW')) { // Old format
             $format = 'Y-m-d\TH:i:s+P';
         }
         parent::__construct(empty($format) ? null : \DateTime::createFromFormat($format, $flexidatetime)->format(\DateTimeInterface::ATOM));
@@ -46,7 +46,7 @@ public function __construct(string $flexidatetime = 'NOW') {
      * @return string
      */
     public function __toString() {
-        return $this->isNull ? null : $this->format(RO::$DateTimeFormat);
+        return $this->isNull ? '' : $this->format(RO::$DateTimeFormat);
     }
 
 }