Added support for PHP 8.1

- Fixed "Passing null to parameter 1 ($version) of type string is deprecated"
- Updated unit tests

src/UXML.php

@@ -196,7 +196,13 @@ public function asText(): string {
      * @return string                XML string
      */
     public function asXML(?string $version="1.0", string $encoding="UTF-8", bool $format=true): string {
-        $doc = new DOMDocument($version, $encoding);
+        $doc = new DOMDocument();
+        if ($version === null) {
+            $doc->xmlStandalone = true;
+        } else {
+            $doc->xmlVersion = $version;
+        }
+        $doc->encoding = $encoding;
         $doc->formatOutput = $format;
         $doc->appendChild($doc->importNode($this->element, true));
         $res = ($version === null) ? $doc->saveXML($doc->documentElement) : $doc->saveXML();
@@ -209,6 +215,6 @@ public function asXML(?string $version="1.0", string $encoding="UTF-8", bool $fo
      * @inheritdoc
      */
     public function __toString(): string {
-        return $this->asXML(null, '', false);
+        return $this->asXML(null, 'UTF-8', false);
     }
 }

tests/UXMLTest.php

@@ -34,6 +34,19 @@ public function testCanHandleSpecialCharacters(): void {
         UXML::newInstance('Test&Fail', 'Not a valid tag name');
     }
 
+    public function testCanExportXml(): void {
+        $xml = UXML::newInstance('Root');
+        $this->assertEquals('<Root/>', (string) $xml);
+        $this->assertEquals('<Root/>', $xml->asXML(null));
+        $this->assertEquals("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<Root/>\n", $xml->asXML());
+        $this->assertEquals("<?xml version=\"1.1\" encoding=\"ISO-8859-1\"?>\n<Root/>\n", $xml->asXML('1.1', 'ISO-8859-1'));
+
+        $xml = UXML::fromString('<a><b>1</b><b>2</b></a>');
+        $this->assertEquals("<a>\n  <b>1</b>\n  <b>2</b>\n</a>", $xml->asXML(null));
+        $this->assertEquals('<a><b>1</b><b>2</b></a>', (string) $xml);
+        $this->assertEquals('<a><b>1</b><b>2</b></a>', $xml->asXML(null, 'UTF-8', false));
+    }
+
     public function testCanLoadXml(): void {
         $source  = "<fruits>";
         $source .= "<fruit>Banana</fruit>";