Use placeholderRes/errorRes if url is null

It would be cool if passing null url would use placeholder drawable or error drawable if set. Right now it defeats the purpose of fluent api when you have to do something like:

if (imageUrl != null) { it.load(imageUrl) { placeholder(placeholderRes) } } else { it.setImageResource(placeholderRes) }

[colinrtwhite]

@mlilienberg Great point. I think it makes sense to use the same API as Glide. i.e.:

imageView.load(itemModel.imageUrl) {
   placeholder(R.drawable.ic_placeholder)
   error(R.drawable.ic_error)
   fallback(R.drawable.ic_error)
}

Similar to placeholder and error, you should be able to set the default fallback on your ImageLoader.

[colinrtwhite]

This is now supported in master. To get the fix asap you can depend on 0.9.0-SNAPSHOT.

NOTE: There might be minor behaviour changes to the feature before 0.9.0 stable.