belongs_to defaults to required. setting some to optional

app/models/crop.rb

@@ -17,8 +17,8 @@ class Crop < ApplicationRecord
   has_many :harvests
   has_many :plant_parts, -> { uniq.reorder("plant_parts.name") }, through: :harvests
   belongs_to :creator, class_name: 'Member'
-  belongs_to :requester, class_name: 'Member'
-  belongs_to :parent, class_name: 'Crop'
+  belongs_to :requester, class_name: 'Member', optional: true
+  belongs_to :parent, class_name: 'Crop', optional: true
   has_many :varieties, class_name: 'Crop', foreign_key: 'parent_id'
   has_and_belongs_to_many :posts # rubocop:disable Rails/HasAndBelongsToMany
 

app/models/harvest.rb

@@ -35,7 +35,7 @@ class Harvest < ApplicationRecord
   belongs_to :crop
   belongs_to :owner, class_name: 'Member', counter_cache: true
   belongs_to :plant_part
-  belongs_to :planting
+  belongs_to :planting, optional: true
 
   ##
   ## Scopes

app/models/post.rb

@@ -6,7 +6,7 @@ class Post < ApplicationRecord
   #
   # Relationships
   belongs_to :author, class_name: 'Member'
-  belongs_to :forum
+  belongs_to :forum, optional: true
   has_many :comments, dependent: :destroy
   has_and_belongs_to_many :crops # rubocop:disable Rails/HasAndBelongsToMany
   # also has_many notifications, but kinda meaningless to get at them