`nil` not handled in `Bundleup::Colors.strip`

Nobody has claimed this yet.

I got `'Bundleup::Colors.strip': undefined method 'gsub' for nil (NoMethodError)` running `bundleup`

Added some debug code like below (`lib/bundleup/report.rb`
```ruby
def max_length_of_each_column(rows)
puts "rows.inspect"
puts rows.inspect
Array.new(rows.first.count) do |i|
rows.map { |values| Colors.strip(values[i]).length }.max
end
end
```

and results in
```
rows.inspect
[["database_cleaner-core", "2.0.1", "→", "2.1.0", ":", "pinned at", "2026-06-01", nil, ""], ["i18n-js", "3.9.2", "→", "4.2.4", ":", "pinned at", "~>", "3.9.2", "\e[0;90;49m# Export translations to JS\e[0m"], ["ruby_jard", "0.2.0", "→", "0.3.1", ":", "pinned at", ">=", "0", "\e[0;90;49m# https://rubyjard.org`\e[0m"], ["rugged", "1.6.5", "→", "1.9.4", ":", "pinned at", "~>", "1.6.5", "\e[0;90;49m# https://github.com/prontolabs/pronto/issues/447\e[0m"], ["tty-prompt", "0.22.0", "→", "0.23.1", ":", "pinned at", ">=", "0.22.0", ""], ["twitter-text", "1.14.7", "→", "3.1.0", ":", "pinned at", "~>", "1.14.7", "\e[0;90;49m# For URL extraction from text\e[0m"], ["unf", "0.1.4", "→", "0.2.0", ":", "pinned at", "2024-08-17", nil, ""], ["useragents", "0.1.4", "→", "0.1.6", ":", "pinned at", " =", "0.1.4", "\e[0;90;49m# New versions got bug and got extra nokogiri dependency\e[0m"]]
```

I dunno what generates those `nil`s, the Gemfile does not reference them (dependencies of Gemfile dependenceis

Start in lib/bundleup/report.rb at max_length_of_each_column and trace how its rows reach Bundleup::Colors.strip. Reproduce the failure with bundleup using the reported rows, then verify that nil values no longer raise NoMethodError and the command completes successfully.

Written by the indexing model from the issue text.