Can't calculate first harvest if there are no harvests

app/models/planting.rb

@@ -114,6 +114,7 @@ class Planting < ActiveRecord::Base
   end
 
   def update_harvest_days
+    return unless harvests.size.positive?
     # how long ago was this planted
     first_harvest = (harvests.first.harvested_at - planted_at).to_i
     last_harvest = finished? ? (harvests.last.harvested_at - planted_at).to_i : nil