FIX: When running the wizard and using a custom theme, fallback to the color_scheme name if the base_scheme_id is nil (#8236)

spec/components/wizard/wizard_builder_spec.rb

@@ -162,7 +162,21 @@ describe Wizard::Builder do
       end
     end
 
-    describe "when the default them hass been override" do
+    describe "when the default theme has been override and the color scheme doesn't have a base scheme" do
+      let(:color_scheme) { Fabricate(:color_scheme, base_scheme_id: nil) }
+
+      before do
+        SiteSetting.default_theme_id = theme.id
+        theme.update(color_scheme: color_scheme)
+      end
+
+      it 'fallbacks to the color scheme name' do
+        expect(field.required).to eq(false)
+        expect(field.value).to eq(color_scheme.name)
+      end
+    end
+
+    describe "when the default theme has been override" do
       before do
         theme.set_default!
       end