UnknownTarget and error codes

[Glen Daniels]

Hi Abdera-devs!

I'm building something based off the AbstractEntityCollectionProvider, 
so I've got my custom TargetResolver looking through the backend data 
store to figure out the correct type of thing for the requested URI.  I 
can't just use a standard pattern/route here because I support 
hierarchical collections of arbitrary names, so in one case "foo/bar" 
might be an entry and in another it might be a collection.

So essentially I look up the given path in my backend, and if I don't 
find it I return null from resolve().

Can anyone explain to me the rationale behind returning an "unknown 
method" error when a null target is returned from a TargetResolver?  It 
would seem to my Abdera-beginner's eye that a 404 would be much more 
natural here.  Right now in order to get a 404 I have to do something 
like a) notice that the requested thing doesn't exist in the 
TargetResolver, but return a valid Target anyway after setting some 
property in the context - then b) check for that property in my 
overriden getEntry() method and throw a 404 there.

Thanks,
--Glen