Problems with `html_safe` in Rails 5

[Tresky]

I recently updated my application to Rails 5.0.6 and was rerunning the test suite when formtastic-bootstrap threw an error relating to the html_safe command.

Failure/Error: <%=  ep.input :media_link, input_html: { onBlur: 'onYouTubeIframeAPIReady()' }, label: t('activerecord.attributes.engagement_player.media_link') %>

ActionView::Template::Error:
    undefined method `html_safe' for Formtastic::Util:Module
    Did you mean?  html_safe?

I dived into the code for this gem and line 14 (the line that the full error report says is the issue; see pastebin link below) doesn't even have html_safe on it, so I'm not sure where the error message is coming from. Anyone have any insight into this issue or have experienced anything similar?

lib/formtastic-bootstrap/inputs/base/wrapping.rb
----------------
08 | def bootstrap_wrapping(&block)
09 |   form_group_wrapping do
10 |     label_html <<
11 |       template.content_tag(:span, :class => 'form-wrapper') do
12 |         input_content(&block) <<
13 |         hint_html(:block) <<
14 |         error_html(:block)     # Problem line
15 |       end
16 |   end
17 | end

Here's a Pastebin of the entirety of the error message generated: https://pastebin.com/LyLXcUcx

Thanks, Tresky

EDIT: Formatting

[Genkilabs]

Still an issue on Rails 6.0.0.rc1