Show error message if no radio button for vaccine selected

app/controllers/vaccinations_controller.rb

@@ -56,9 +56,12 @@ def create
         &:reset!
       )
 
-    @draft_vaccination_record.assign_attributes(create_params)
+    @draft_vaccination_record.patient_session = @patient_session
 
-    if @draft_vaccination_record.save
+    if create_params.nil?
+      @draft_vaccination_record.errors.add(:administered, :blank)
+      render "patient_sessions/show", status: :unprocessable_entity
+    elsif @draft_vaccination_record.update(create_params)
       steps = @draft_vaccination_record.wizard_steps
 
       steps.delete(:date_and_time)
@@ -130,17 +133,16 @@ def vaccination_record_params
         :programme_id,
         :vaccine_id
       )
-      .merge(
-        patient_session: @patient_session,
-        performed_at: Time.current,
-        performed_by_user: current_user
-      )
+      .merge(performed_at: Time.current, performed_by_user: current_user)
   end
 
   def create_params
-    if vaccination_record_params[:administered] == "true"
+    administered = vaccination_record_params[:administered]
+    return if administered.blank?
+
+    if administered == "true"
       create_params =
-        if delivery_site_param_other?
+        if vaccination_record_params[:delivery_site] == "other"
           vaccination_record_params.except(:delivery_site, :delivery_method)
         else
           vaccination_record_params
@@ -155,10 +157,6 @@ def create_params
     end
   end
 
-  def delivery_site_param_other?
-    vaccination_record_params[:delivery_site] == "other"
-  end
-
   def set_session
     @session =
       policy_scope(Session).includes(:location).find_by!(

app/models/draft_vaccination_record.rb

@@ -96,9 +96,13 @@ def wizard_steps
   end
 
   def administered?
+    return nil if outcome.nil?
     outcome == "administered"
   end
 
+  # So that a form error matches to a field in this model
+  alias_method :administered, :administered?
+
   def batch
     BatchPolicy::Scope.new(@current_user, Batch).resolve.find_by(id: batch_id)
   end

config/locales/en.yml

@@ -192,7 +192,7 @@ en:
         draft_vaccination_record:
           attributes:
             administered:
-              inclusion: Choose if they got the vaccine
+              blank: Choose if they got the vaccine
             batch_id:
               blank: Choose a batch
               incorrect_vaccine: Choose a batch of the %{vaccine_brand} vaccine