New robots allow property missing from existing documents in client projects throws NPE

In client projects with existing Robots documents the robotstxt:allow property won't be present until those documents are edited or updated with a groovy script.

This throws an NPE in org.onehippo.forge.robotstxt.annotated.Section line 45

return Arrays.asList(allows); because allows is null for existing documents.

This can be replaced with something like 

return allows != null ? Arrays.asList(allows) : Arrays.asList();

Reproduced with clean archetype on v15.2.2 - see screenshot attached