Fix page invalidation when no form set

app/models/case_log.rb

@@ -226,6 +226,8 @@ private
   end
 
   def reset_invalidated_dependent_fields!
+    return unless form
+
     form.invalidated_page_questions(self).each do |question|
       public_send("#{question.id}=", nil) if respond_to?(question.id.to_s)
     end

spec/models/case_log_spec.rb

@@ -656,6 +656,10 @@ RSpec.describe CaseLog do
       case_log.update(age1: 25)
     end
 
+    it "validates start date" do
+      expect(validator).to receive(:validate_startdate)
+    end
+
     it "validates ages" do
       expect(validator).to receive(:validate_person_1_age)
       expect(validator).to receive(:validate_household_number_of_other_members)
@@ -1039,6 +1043,14 @@ RSpec.describe CaseLog do
         expect(case_log.cbl).to eq("Yes")
       end
     end
+
+    context "when the case log does not have a valid form set yet" do
+      let(:case_log) { FactoryBot.create(:case_log) }
+
+      it "does not throw an error" do
+        expect { case_log.update(startdate: Time.zone.local(2015, 1, 1)) }.not_to raise_error
+      end
+    end
   end
 
   describe "paper trail" do