/usr/bin/do-release-upgrade:11:_gtk_style_provider_private_get_settings:gtk_css_value_initial_compute:gtk_css_static_style_compute_value:_gtk_css_lookup_resolve:gtk_css_static_style_new_compute

[errors.ubuntu.com bug bridge]

The Ubuntu Error Tracker has been receiving reports about a problem regarding ubuntu-release-upgrader. This problem was most recently seen with package version 1:17.10.11, the problem page at https://errors.ubuntu.com/problem/4bc5ba629c67272bfaabc2961825ea092b857b09 contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.