Drupal\migrate\Plugin\migrate\process\MigrationLookup::skipOnEmpty() is removed.

Protected method Drupal\migrate\Plugin\migrate\process\MigrationLookup::skipOnEmpty() is removed in Drupal 8.7.0. Plugins extending this class should use ::skipInvalid() instead.

Background:

The migration_lookup plugin throws an exception when called with invalid lookup ids. The plugin errantly used an empty() check to determine if lookup ids were invalid, but this caused the plugin to throw an exception on valid, yet technically empty keys like 0.

This behavior is fixed in Drupal 8.7, and the method containing the skipping logic was renamed for clarity.

Before:

      if (!is_array($value)) {
        $value = [$value];
      }
      $this->skipOnEmpty($value);
      $source_id_values[$lookup_migration_id] = $value;

After:

      if (!is_array($value)) {
        $value = [$value];
      }
      $this->skipInvalid($value);
      $source_id_values[$lookup_migration_id] = $value;