increase time_zone robustness

app/models/user.rb

@@ -406,7 +406,7 @@ def pref
   end
 
   def time_zone
-    @time_zone ||= (pref.time_zone.blank? ? nil : ActiveSupport::TimeZone[pref.time_zone])
+    @time_zone ||= ActiveSupport::TimeZone[pref.time_zone] || ActiveSupport::TimeZone["Etc/UTC"]
   end
 
   def reload(*)

spec/models/user_spec.rb

@@ -823,6 +823,39 @@ def build_user_double_with_expired_password(is_expired)
     end
   end
 
+  describe "#time_zone" do
+    let(:user) { build(:user, preferences:) }
+
+    context "with an existing time zone in the prefs" do
+      let(:preferences) { { "time_zone" => "Europe/Athens" } }
+
+      it "returns the matching ActiveSupport::TimeZone" do
+        expect(user.time_zone)
+          .to eql ActiveSupport::TimeZone["Europe/Athens"]
+      end
+    end
+
+    context "with an invalid time zone" do
+      # Would need to be Etc/UTC or UTC to be valid
+      let(:preferences) { { "time_zone" => "utc" } }
+
+      it "returns the utc ActiveSupport::TimeZone" do
+        expect(user.time_zone)
+          .to eql ActiveSupport::TimeZone["Etc/UTC"]
+      end
+    end
+
+    context "without a time zone" do
+      # Would need to be Etc/UTC or UTC to be valid
+      let(:preferences) { {} }
+
+      it "returns the utc ActiveSupport::TimeZone" do
+        expect(user.time_zone)
+          .to eql ActiveSupport::TimeZone["Etc/UTC"]
+      end
+    end
+  end
+
   describe "#find_by_mail" do
     let!(:user1) { create(:user, mail: "[email protected]") }
     let!(:user2) { create(:user, mail: "[email protected]") }