Fallback to crop specific photos in PhotoCapable thumbnail_url

app/models/concerns/photo_capable.rb

@@ -18,9 +18,11 @@ def default_photo
     def thumbnail_url
       df = default_photo
 
-      return unless df
-
-      df.source == 'flickr' ? df.fullsize_url : df.thumbnail_url
+      if df
+        df.source == 'flickr' ? df.fullsize_url : df.thumbnail_url
+      elsif respond_to?(:crop) && crop.present?
+        crop.thumbnail_url
+      end
     end
 
     def most_liked_photo

app/models/photo_association.rb

@@ -28,6 +28,7 @@ def set_crop
 
   def photo_and_item_have_same_owner
     return if photographable_type == 'Crop'
+    return if photographable.blank?
 
     errors.add(:photo, :photo_owner_mismatch) unless photographable.owner_id == photo.owner_id
   end

spec/models/planting_spec.rb

@@ -421,6 +421,25 @@ def one_hundred_day_old_planting
       planting.photos << @photo2
       expect(planting.default_photo).to eq @photo2
     end
+
+    describe '#thumbnail_url' do
+      let(:crop_photo) { create(:photo) }
+
+      it 'returns its own default photo if present' do
+        expect(planting.thumbnail_url).to eq photo.fullsize_url
+      end
+
+      it 'falls back to crop default photo if no planting photo is present' do
+        planting_without_photo = create(:planting, crop:)
+        PhotoAssociation.create!(photo: crop_photo, photographable: crop)
+        expect(planting_without_photo.thumbnail_url).to eq crop_photo.fullsize_url
+      end
+
+      it 'returns nil if neither planting nor crop has a photo' do
+        planting_without_photo = create(:planting, crop:)
+        expect(planting_without_photo.thumbnail_url).to be_nil
+      end
+    end
   end
 
   context 'interesting plantings' do