Make it possible to skip empty migration destinations

Besides testing, the handbook needs upgrading with ample warning on how this actually does not import data.

Another option without this patch is:

-
plugin: static_map
bypass: TRUE
map:
  '': null
-
plugin: skip_on_empty
method: process
-
plugin: migration
migration: foo

But I like the patch. It makes the DX a lot easier.

You can't; this patch skips stubbing -- this means phenaproxima was right when he said it's cleaner to call it no_stubbing

Actually, after looking at the migration plugin, I don't think #8 is a possibility. Let's go with it.

We already have "no_stub" which does the same thing in the destination, these two names could be easily confused, shall we make them the same?

Well. I put them on the destination because I thought it's the destination which can determine it just can not be stubbed. But perhaps we do need both? Like, it is possible in general for a destination to be stubbed but in specifics we do not want so?

Well. I put them on the destination because I thought it's the destination which can determine it just can not be stubbed. But perhaps we do need both? Like, it is possible in general for a destination to be stubbed but in specifics we do not want so?

I think in general it makes sense for the destination to have the settings when you're talking about the current migration but dawehner's problem here is that he wants to allow broken/missing data from another migration that is referenced. I think renaming to no_stub the same as the destinations would be more consistent and then the patch here looks good.

+++ b/core/modules/migrate/tests/src/Unit/process/MigrationTest.php
@@ -0,0 +1,91 @@
+namespace Drupal\Tests\migrate\Unit\process;
+use Drupal\Core\Entity\EntityStorageInterface;

Missing new line

Let's do this.

I think renaming to no_stub the same as the destinations would be more consistent

I still think this would be better. Even if skip_stubbing is a better name, consistency is the most important bit for me.

Responding to #17.

Committed/pushed to 8.1.x and cherry-picked to 8.0.x. Thanks!