Passing chat_postMessage attachments=null will cause "Copy Link" in Slack not to unfurl.

I was so confused on this one I contacted someone at slack support.

At some point in the last several weeks, we noticed that our Copy Link for messages from from this ruby client would no longer unfurl (create a preview of the original message). This was problematic as we value our previews, and click on a *.slack.com/archive/.... link to see the message (and taking you out of context) isn't a good user experience.

After debugging the output in faraday, I noticed that our attachments was nil but still being added to the request body.

self.SlackClient.chat_postMessage(
  channel: channel,
  text: msg,
  as_user: true,
  link_names: true,
  thread_ts: thread_ts,
  attachments: attachments #passed in as nil
)

I believe in the past this wasn't an issue, but in the last several weeks the behaviour has changed. To fix this I just stopped sending the attachments argument if it was nil.

# see keyword_args: https://www.justinweiss.com/articles/fun-with-keyword-arguments/
keyword_args = {
  channel: channel,
  text: msg,
  as_user: true,
  link_names: true,
}
keyword_args[thread_ts] = thread_ts unless thread_ts.nil?
keyword_args[attachments] = attachments unless attachments.nil?
self.SlackClient.chat_postMessage(**keyword_args)

I was thinking someone might want to filter out any nil arguments from the request body before sending it out (or throw error)

Cheers,
Jason.

Start at the Ruby client's chat_postMessage request-building path and inspect the Faraday request body when attachments is nil. Reproduce the call described in the issue, then verify that the selected handling of nil arguments prevents the Slack Copy Link unfurling regression.