Drupal 6 to 8 cck imagefield

Hi,

I tried to migrate my drupal 6 site to drupal 8.
Everything works fine except CCK imagefield.

All fields have been migrated, but without any data - all filefields are empty.

I have migrated my site using:
drush migrate-upgrade --migration-prefix="" --legacy-db-url=mysql://root:user@localhost/databaseold

Results:

Upgrading d6_date_formats
Upgrading d6_dblog_settings
Upgrading d6_filter_format
Missing filter plugin: filter_null. [error]
Missing filter plugin: filter_null. [error]
Upgrading d6_imagecache_presets
Upgrading d6_language_types
Upgrading d6_menu
Upgrading d6_path_redirect
Upgrading d6_search_settings
Upgrading d6_system_cron
Upgrading d6_system_date
Upgrading d6_system_file
Upgrading d6_system_performance
Upgrading d6_url_alias
Upgrading d6_user_mail
Upgrading d6_user_settings
Upgrading file_settings
Upgrading locale_settings
Upgrading menu_settings
Upgrading search_page
Upgrading system_image
Upgrading system_image_gd
Upgrading system_logging
Upgrading system_maintenance
Upgrading system_rss
Upgrading system_site
Upgrading taxonomy_settings
Upgrading text_settings
Upgrading update_settings
Upgrading block_content_type
Upgrading d6_menu_links
Upgrading block_content_body_field
Upgrading d6_custom_block
Upgrading d6_user_role
Upgrading d6_block
Upgrading d6_comment_type
Upgrading d6_comment_field
Upgrading d6_node_type
Upgrading d6_comment_field_instance
Upgrading d6_comment_entity_display
Upgrading d6_comment_entity_form_display_subject
Upgrading language
Upgrading default_language
Upgrading d6_file
Upgrading d6_user_picture_file
Upgrading user_picture_field
Upgrading user_picture_field_instance
Upgrading user_picture_entity_display
Upgrading user_picture_entity_form_display
Upgrading d6_user
Upgrading d6_node_settings
Upgrading d6_field
Upgrading d6_field_instance
Upgrading d6_field_instance_widget_settings
Upgrading d6_view_modes
Upgrading d6_field_formatter_settings
Upgrading d6_upload_field
Upgrading d6_node:blog
Upgrading d6_node:comics
Upgrading d6_node:comparison
Upgrading d6_node:english
Upgrading d6_node:games
Upgrading d6_node:groups
Upgrading d6_node:madfaqs
Upgrading d6_node:madpictures
Upgrading d6_node:madring
Upgrading d6_node:minireview
Upgrading d6_node:news
Upgrading d6_node:page
Upgrading d6_node:poll
Upgrading d6_node:profile
Upgrading d6_node:questions
Upgrading d6_node:quotes
Upgrading d6_node:story
Upgrading d6_node:vs
Upgrading d6_comment_entity_form_display
Upgrading d6_comment
Upgrading d6_field_group_entity_form_display
Upgrading d6_field_group_entity_view_display
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Illegal string offset 'format' FieldGroup.php:116 [warning]
Upgrading d6_language_content_settings
Upgrading language_prefixes_and_domains
Upgrading d6_language_negotiation_settings
Upgrading d6_node_setting_promote
Upgrading d6_node_setting_sticky
Upgrading d6_node_setting_status
Upgrading d6_node_revision:blog
Upgrading d6_node_revision:comics
Upgrading d6_node_revision:comparison
Upgrading d6_node_revision:english
Upgrading d6_node_revision:games
Upgrading d6_node_revision:groups
Upgrading d6_node_revision:madfaqs
Upgrading d6_node_revision:madpictures
Upgrading d6_node_revision:madring
Upgrading d6_node_revision:minireview
Upgrading d6_node_revision:news
Upgrading d6_node_revision:page
Upgrading d6_node_revision:poll
Upgrading d6_node_revision:profile
Upgrading d6_node_revision:questions
Upgrading d6_node_revision:quotes
Upgrading d6_node_revision:story
Upgrading d6_node_revision:vs
Upgrading d6_taxonomy_vocabulary
Upgrading d6_vocabulary_field
Upgrading d6_vocabulary_field_instance
Upgrading d6_vocabulary_entity_form_display
Upgrading d6_vocabulary_entity_display
Upgrading d6_taxonomy_term
Upgrading d6_term_node:1
Upgrading d6_term_node:3
Upgrading d6_term_node:6
Upgrading d6_term_node:8
Upgrading d6_term_node:9
Upgrading d6_term_node:10
Upgrading d6_term_node:11
Upgrading d6_term_node:13
Upgrading d6_term_node:14
Upgrading d6_term_node_revision:1
Upgrading d6_term_node_revision:3
Upgrading d6_term_node_revision:6
Upgrading d6_term_node_revision:8
Upgrading d6_term_node_revision:9
Upgrading d6_term_node_revision:10
Upgrading d6_term_node_revision:11
Upgrading d6_term_node_revision:13
Upgrading d6_term_node_revision:14
Upgrading user_profile_field
Upgrading user_profile_field_instance
Upgrading user_profile_entity_display
Upgrading user_profile_entity_form_display
Upgrading d6_profile_values
Upgrading d6_user_contact_settings

Is there any clear procedure how to migrate imagefield data?

Thanks