Fix problem when event has no max participants limit

Ghost Userrequested to merge
fix/events-no-max-participants into master

Previous behaviour

Steps to reproduce:

  1. Create event without max participants
  2. Go to the event API detail page
  3. Error

New behaviour

Steps to validate that it works:

  1. Create event without max participants
  2. Go to the event API detail page
  3. No error

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