Fix sanitize bug when no arguments are specified

Author: QuickWrite

src/main/java/net/quickwrite/fluent4j/ast/placeable/base/FluentFunction.java

@@ -93,7 +93,9 @@ private Pair<String, FluentElement> getArgument(final StringSlice content) {
      * @return The sanitized arguments of the function
      */
     protected FluentArgs getArguments(final DirectFluentBundle bundle, final FluentArgs arguments) {
-        this.arguments.sanitize(bundle, arguments);
+        if (this.arguments != null)
+            this.arguments.sanitize(bundle, arguments);
+
         return this.arguments;
     }