Double splat cannot handle nil

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Last Updated: 2021-05-16

I had the following code (pay attention to the tracking_info parameter)

def add_email_to_list(email:, tracking_info:)
  EmailSubscriber.find_by(email: email) || EmailSubscriber.new(
    email: email, **tracking_info
  )
  ...
end

I called with the following

add_email_to_list(email: 'j@example.com', tracking_info: session[:tracking_info])

The key is that sometimes the session[:tracking_info] was nil. In this case the function fails, not knowing how to apply ** to nil.

Defaulting to an empty hash at point of call is needed to fix:

def add_email_to_list(email:, tracking_info:)
  EmailSubscriber.find_by(email: email) || EmailSubscriber.new(
    # New code in parentheses below:
    email: email, **(tracking_info || {})
  )
  ...
end