diff --git a/src/XMLBuild.php b/src/XMLBuild.php
index dce4562..8db197e 100644
--- a/src/XMLBuild.php
+++ b/src/XMLBuild.php
@@ -100,7 +100,7 @@ public static function attributeValue($value)
 
         // REC-xml/#AVNormalize - preserve
         // REC-xml/#sec-line-ends - preserve
-        $buffer = preg_replace_callback('~\r\n|\r(?!\n)|\t~', array('self', 'numericEntitiesSingleByte'), $buffer);
+        $buffer = preg_replace_callback('~\r\n|\r(?!\n)|\t~', array('XMLBuild', 'numericEntitiesSingleByte'), $buffer);
 
         return htmlspecialchars($buffer, ENT_QUOTES, 'UTF-8', false);
     }
diff --git a/src/XMLReaderNode.php b/src/XMLReaderNode.php
index 0ef42e1..6b41206 100644
--- a/src/XMLReaderNode.php
+++ b/src/XMLReaderNode.php
@@ -212,7 +212,7 @@ public function readOuterXml()
      * @throws BadMethodCallException
      * @return DOMNode
      */
-    public function expand(DOMNode $baseNode = null)
+    public function expand(?DOMNode $baseNode = null)
     {
         if (null === $baseNode) {
             $baseNode = new DomDocument();