Conditionals for blank or deleted values?

[versatilehuman]

• Blank value in maintenance_div in points_of_interest junked the poi alerts page.
• Deleted user is preventing export of alerts (#248)

Are there any other places we need to implement conditionals to tighten things up?

[gisdevcc]

A fix for the maintenance_div in poi alertts issue is fixed with https://github.com/fpdcc/trailsyserver/commit/9ab09c071c4e18032dc1ae700f7239db4c5f5a6d

Deferring larger review for later