[Misc] Protect against null content

xwiki-platform-core/xwiki-platform-rendering/xwiki-platform-rendering-parser/src/main/java/org/xwiki/rendering/internal/parser/DefaultContentParser.java

@@ -59,7 +59,7 @@ public class DefaultContentParser implements ContentParser
     @Override
     public XDOM parse(String content, Syntax syntax) throws ParseException, MissingParserException
     {
-        return getParser(syntax).parse(new StringReader(content));
+        return getParser(syntax).parse(new StringReader(content == null ? "" : content));
     }
 
     @Override