Cannot connect to URL

[ihsanfaisal]

I got the following error. I think there is something wrong with httpclient library, but I'm not sure.

cannot connect to  https://hooks.slack.com/services/...
Invalid scheme format:  https

It happens around here

redmine-slack/lib/redmine_slack/listener.rb

Lines 160 to 163 in 1340d83

	client.post_async url, {:payload => params.to_json}
	rescue Exception => e
	Rails.logger.warn("cannot connect to #{url}")
	Rails.logger.warn(e)

My install system specs:

• Redmine 3.4.4.stable
• Rails 4.2.10
• Ruby 2.5.1p57
• Ubuntu 18.04

Any help is appreciated -- thanks.