Update to Drupal 8.0.0 beta 14. For more information, see https://drupal.org/node/2544542

core/modules/node/config/schema/node.source.schema.yml

@@ -0,0 +1,42 @@
+migrate.source.d6_view_mode:
+  type: migrate_source_sql
+  label: 'Drupal 6 view mode'
+  mapping:
+    constants:
+      type: mapping
+      label: 'Constants'
+      mapping:
+        targetEntityType:
+          type: string
+          label: 'Target entity type'
+        status:
+          type: boolean
+          label: 'Status'
+
+migrate.source.d6_node_type:
+  type: migrate_source_sql
+  label: 'Drupal 6 node type'
+  mapping:
+    constants:
+      type: migrate_entity_constant
+      label: 'Constants'
+
+migrate.source.d6_node:
+  type: migrate_source_sql
+  label: 'Drupal 6 node'
+  mapping:
+    node_type:
+      # The node type can be specified both as a string ID of a node type or an
+      # array of node type IDs, so there is no way to consistently parse this.
+      type: ignore
+      label: 'Node type'
+
+migrate.source.d6_node_revision:
+  type: migrate_source_sql
+  label: 'Drupal 6 node'
+  mapping:
+    node_type:
+      # The node type can be specified both as a string ID of a node type or an
+      # array of node type IDs, so there is no way to consistently parse this.
+      type: ignore
+      label: 'Node type'