Fixed deprecation warnings about passing null as parameter

Author: derrabus

Parser.php

@@ -616,7 +616,7 @@ private function getNextEmbedBlock(int $indentation = null, bool $inSequence = f
         $data = [];
 
         if ($this->getCurrentLineIndentation() >= $newIndent) {
-            $data[] = substr($this->currentLine, $newIndent);
+            $data[] = substr($this->currentLine, $newIndent ?? 0);
         } elseif ($this->isCurrentLineEmpty() || $this->isCurrentLineComment()) {
             $data[] = $this->currentLine;
         } else {