Issue #3326130 by quietone: Add an example to...

 *       migration: d6_taxonomy_term

 * @endcode

 * If 'parent' is empty, any further processing of the property is skipped and

 * the next process plugin (migration_lookup) will not be run. Combining

 * skip_on_empty and migration_lookup is a typical process pipeline combination

 * for hierarchical entities where the root entity does not have a parent.

 * the next process plugin (migration_lookup) will not be run. If the

 * migration_lookup process is executed it will use 'parent' as the source.

 * Combining skip_on_empty and migration_lookup is a typical process pipeline

 * combination for hierarchical entities where the root entity does not have a

 * parent.

 *

 * @code

 * process:

 *   parent:

 *     -

 *       plugin: skip_on_empty

 *       method: process

 *       source: parent

 *     -

 *       plugin: migration_lookup

 *       migration: d6_taxonomy_term

 *       source: original_term

 * @endcode

 * If 'parent' is empty, any further processing of the property is skipped and

 * the next process plugin (migration_lookup) will not be run. If the

 * migration_lookup process is executed it will use 'original_term' as the

 * source.

 *

 * @see \Drupal\migrate\Plugin\MigrateProcessInterface

 *