If a post has invalid categories, it won't render

[vikingcode]

Forgive me, it's been awhile since I've used Github so I'm not sure how all the cool kids link to stuff properly anymore.

Basically if a post has no category, it'll throw a NullReferenceException when evaluating the permalink. The "offending" line (for lack of a better term) is this:
permalink = permalink.Replace(":categories", string.Join("-", page.Categories.ToArray()));

https://github.com/Code52/pretzel/blob/master/src/Pretzel.Logic/Templating/Context/SiteContextGenerator.cs#L402

Now, I know I could send in a PR but there would be a couple of things to think about:

• A check before hand, if (page.Categories != null) solves the issue, easy done, right? Well, does that then necessitate a check for each of the date properties?
• Investigate why page.Categories isn't initialised, because in theory it is in the constructor for Page.

[laedit]

Thanks for reporting this, but I cannot reproduce the bug: for a post with no categories, the Categories property is well initiated and empty.

Can you indicate some way to reproduce it?

[vikingcode]

Okay, so, I'm an idiot. It's not that my posts have no categories, its that Pretzel didn't pick them up because of incorrect syntax and nulled its on values.

Using the post below as context, page.Categories = header["categories"] as IEnumerable<string>; (ln245 of the same file) comes out as null because in this context I haven't provided multiple categories. Now the key here is my syntax is off - it should be

categories:
-foo
-bah

So the solution is for me to fix my syntax, but the only way I discovered my syntax was off was by digging into the source code of Pretzel. There isn't an error (other than NullValueException) indicating what was wrong.

I think ultimately pretzel should do a "best effort" at delivering a page rather than stopping on an error (obviously depending on the scope of the error!). I think the null value check on L400 would still be a good idea for idiots like me :D What I mean is, sure, categories shouldn't work because my syntax is off, but the rest of the page should at least render by adding that check

---

Here is an example of the YAML front matter thats failing (the rest of the post isn't super relevant)

---
layout: post
title:  "Building a fancier work bench for the mini lathe"
date:  2015-02-11
categories:  video
---

[laedit]

Thanks for the info.
Yeah, I think we can add the check, and also support the "one categories" case.

For info, you can also use the syntax:
categories: [video]