Undefined index: extra_attributes

I am getting the following notice in my PHP error log:

Notice: Undefined index: extra_attributes in [...]/wp-content/plugins/wp-asset-clean-up/classes/OptimiseAssets/CombineJs.php on line 363

Asset Cleanup: 1.3.6.6
WP: 5.4.2 (multisite, the plugin is network enabled)
PHP Version:              7.2.32
MySQL Version:            5.5.5
Webserver Info:           nginx/1.19.1

# Asset CleanUp Configuration 
Has read "Stripping the fat" text:   Yes

Manage in the Dashboard:             No - Assets Meta Box is Hidden - Side Options Meta Box is Hidden
Manage in the Front-end:             Yes
Do not show front-end assets when the URI contains (textarea value):
et_fb=1
ct_builder=true
vc_editable=true
preview_nonce=

Input Fields Style:                  Enhanced
Hide WP Files (from managing):       No
Enable "Test Mode"?                  No

Minify loaded CSS?                   Yes
Minify loaded JS?                    Yes
Combine loaded CSS?                  Yes
Combine loaded JS?                   Yes
CSS/JS Storage Directory:            /home/antelope/webapps/antelope/wp-content/cache/asset-cleanup/ (writable)

Disable Emojis (site-wide)?                       Yes
Disable oEmbed (Embeds) (site-wide)?              Yes
Disable Dashicons if Toolbar (top admin bar) is not showing (site-wide)?         No
Disable Gutenberg CSS Block Editor (site-wide)?   No
Disable jQuery Migrate (site-wide)?               Yes
Disable Comment Reply (site-wide)?                Yes

Remove "Really Simple Discovery (RSD)" link tag?  Yes
Remove "Windows Live Writer" link tag?            Yes
Remove "REST API" link tag?                       Yes
Remove Pages/Posts "Shortlink" tag?               Yes
Remove "Post's Relational Links" tag?             Yes
Remove "WordPress version" meta tag?              Yes
Remove All "generator" meta tags?                 Yes
Remove Main RSS Feed Link?                        Yes
Remove Comment RSS Feed Link?                     Yes

XML-RPC protocol: Disable XML-RPC Completely

# Asset CleanUp: CSS/JS Caching Storage
Total cached files: 42 (542<span style="font-size: 80%; font-weight: 200;">.72</span> KB) of which 17 are CSS/JS assets (539<span style="font-size: 80%; font-weight: 200;">.17</span> KB)

# Asset CleanUp: Database Storage
Table: options
-- Option Name: wpassetcleanup_bulk_unload / Option Value: []
-- Option Name: wpassetcleanup_first_usage / Option Value: 1588860807
-- Option Name: wpassetcleanup_global_data / Option Value: {"styles":{"assets_info":{"dashicons":{"src":"\/wp-includes\/css\/dashicons.min.css"}}},"scripts":{"assets_info":{"jquery-migrate":{"src":"\/wp-includes\/js\/jquery\/jquery-migrate.min.js","ver":"1.4.1"},"comment-reply":{"src":"\/wp-includes\/js\/comment-reply.min.js","args":1}}}}
-- Option Name: wpassetcleanup_global_unload / Option Value: {"styles":["dashicons"],"scripts":["jquery-migrate","comment-reply"]}
-- Option Name: wpassetcleanup_hide_tracking_notice / Option Value: 1
-- Option Name: wpassetcleanup_settings / Option Value: {"wiki_read":"1","dom_get_type":"direct","assets_list_show_status":"fetch_on_click","hide_assets_meta_box":"1","hide_options_meta_box":"1","frontend_show":"1","frontend_show_exceptions":"et_fb=1\r\nct_builder=true\r\nvc_editable=true\r\npreview_nonce=\r\n","assets_list_layout":"by-location","assets_list_layout_plugin_area_status":"expanded","assets_list_layout_areas_status":"expanded","assets_list_inline_code_status":"contracted","input_style":"enhanced","hide_from_side_bar":"1","fetch_cached_files_details_from":"disk","clear_cached_files_after":"7","minify_loaded_css":"1","minify_loaded_css_inline":"1","minify_loaded_css_exceptions":"(.*?)\\.min.css\r\n\/plugins\/wd-instagram-feed\/(.*?).css","combine_loaded_css":"1","combine_loaded_css_for":"guests","combine_loaded_css_exceptions":"\/plugins\/wd-instagram-feed\/(.*?).css","inline_css_files":"1","inline_css_files_below_size":"1","inline_css_files_below_size_input":"3","cache_dynamic_loaded_css":"1","minify_loaded_js":"1","minify_loaded_js_inline":"1","minify_loaded_js_exceptions":"(.*?)\\.min.js\r\n\/plugins\/wd-instagram-feed\/(.*?).js","combine_loaded_js":"1","combine_loaded_js_for":"guests","combine_loaded_js_exceptions":"\/plugins\/wd-instagram-feed\/(.*?).js","inline_js_files_below_size_input":"3","move_scripts_to_body_exceptions":"\/\/cdn.ampproject.org\/","cache_dynamic_loaded_js":"1","disable_emojis":"1","disable_oembed":"1","remove_rsd_link":"1","remove_wlw_link":"1","remove_rest_api_link":"1","remove_shortlink":"1","remove_posts_rel_links":"1","remove_wp_version":"1","remove_generator_tag":"1","remove_main_feed_link":"1","remove_comment_feed_link":"1","remove_html_comments":"1","google_fonts_combine":"1","google_fonts_preconnect":"1","disable_xmlrpc":"disable_all"}

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