Incorrect error when adding issue to epic multiple times

Summary

When adding an issue to an epic, that is already linked, the error displays incorrect information: Screen_Shot_2019-10-08_at_9.58.25_AM

Error message should state something similar to: "Issue already linked to this Epic"

Perhaps it should be a yellow banner instead of red as it isn't a hard failure?

Steps to reproduce

  1. Add an issue to an Epic via the Epic's Add Issue option.
  2. Attempt to add the same issue via the same method
  3. View error

What is the expected correct behavior?

  1. Proper error message should be displayed to reduce user confusion on why the action failed