d6_taxonomy_term migrate fails when the parent term has not been already migrated

Good work, set to "Needs review" so the bot can run the test suite.

The patch fixes the problem for me nicely! Great work!! Using a stub entry until the migration ran over the corresponding taxonomy term is a great idea!

+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityTaxonomyTerm.php
@@ -0,0 +1,34 @@
+use Drupal\Core\Entity\EntityManagerInterface;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\State\StateInterface;
+use Drupal\migrate\Entity\MigrationInterface;
+use Drupal\migrate\Plugin\MigratePluginManager;
...
+use Symfony\Component\DependencyInjection\ContainerInterface;

Note: Just this single class is neeed, all other use statements can be removed.

Removed use statements plus a few other minor changes.

Patch tests this casuistic, and #8 has been cleaned up. So RTBC.
Updated issue title.

+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityTaxonomyTerm.php
@@ -0,0 +1,29 @@
+ *   id = "entity:taxonomy_term"

We only need to specify a class with a plugin id and it overrides entity:*? I <3 this feature.

Yeah, indeed, this is really cool.

Thanks for testing the migrate path for D8!

Committed and pushed to 8.x. Thanks!

Tested against a real-world D6 site - 31 vocabularies ~4500 terms and some hierarchical with multiple parents
Get the same Integrity constraint violation, when it comes to migrating terms with multiple parents.
eg: in d6 term_hierarchy
|tid|parent|
|13|0|
|14|13|
|15|13|
|16|0|
|17|13|
|18|13|
|19|17|
|19|20|
|20|13|

Preparing for a D6 to D8 migration and while the migration completes, taxonomy terms are not fully migrated. Vocabularies are migrated, and then a few (7) terms succeed before returning the following error:

Running d6_taxonomy_term ok
SQLSTATE23000: Integrity constraint violation: 1048 Column 'name' cannot be null: INSERT INTO {taxonomy_term_field_data} (tid, vid, langcode, name, description__value, description__format, weight, error
changed, default_langcode) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5,
:db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8); Array
(
:db_insert_placeholder_0 => 443
:db_insert_placeholder_1 => author
:db_insert_placeholder_2 => en
:db_insert_placeholder_3 =>
:db_insert_placeholder_4 =>
:db_insert_placeholder_5 =>
:db_insert_placeholder_6 => 0
:db_insert_placeholder_7 => 1431101967
:db_insert_placeholder_8 => 1
)

I thought it might be a data issue, since this was marked as fixed in the latest release. I found one term missing a name, but it was not related to the above error, and deleting it from the DB had no affect.
Just to see what would happen, I modified the database tables to allow for NULL values:

ALTER TABLE taxonomy_term_data CHANGE vid vid varchar(32) DEFAULT NULL;
ALTER TABLE taxonomy_term_field_data CHANGE name name varchar(255) DEFAULT NULL;
ALTER TABLE taxonomy_term_field_data CHANGE vid vid varchar(32) DEFAULT NULL;
ALTER TABLE taxonomy_term_field_data CHANGE weight weight int(11) DEFAULT NULL;

At which point the taxonomy terms did migrate, the content types had the appropriate taxonomy term fields, but no taxonomy terms were applied to any content. I also received the following error:

Failed to lookup array (                                                                                                                                                                                              [error]
  0 => 'text',
  1 => 'hidden',
) in the static map.

This site has 5700+ nodes, 6 vocabularies, and 490 terms in term_data. I've posted in this issue because it seems to be the same problem, but will start a new bug report if needed.

Looks like this needs to be re-rolled against the current dev? /core/modules/migrate_drupal/src/Tests/Dump/Drupal6TaxonomyTerm.php doesn't exist in the current version, so this patch does not apply...

It looks as though my above issue was related to using the beta10 version rather than pulling the current dev version from git.
After rebuilding and re-running a migrate with the current dev version I no longer get this error, and taxonomy terms do migrate.
There are other issues, but we'll post those in the appropriate threads.
Sorry for the confusion.

Migration (Drupal 6 to Drupal-8.1.7) does not bring any taxonomy terms and content taxonomy fields. I get the error
Failed to lookup field type array ( 0 => 'content_taxonomy', 1 => 'default', ) in the static map.
Any help would be highly appreciated !