Fix review comments: apply coding guidelines and add missing tests

- Add @nullable to GlobalScheduleProperties.defaultTimezone() (L-1)
- Update scheduleTimezone @PARAM Javadoc in EndpointGateEndpoint and
  ReactiveEndpointGateEndpoint to reflect fallback chain (M-1)
- Update additional-spring-configuration-metadata.json gate-level
  timezone description to reflect global default fallback (M-2)
- Add updateGate_usesDefaultScheduleTimezone and
  updateGate_usesExplicitTimezone tests to ReactiveEndpointGateEndpointTest (H-1)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kukv

spring/actuator/src/main/java/net/brightroom/endpointgate/spring/actuator/endpoint/EndpointGateEndpoint.java

@@ -108,7 +108,8 @@ public EndpointGateEndpointResponse gate(@Selector String gateId) {
    * @param scheduleStart the schedule start time, or {@code null} if only an end time is needed
    * @param scheduleEnd the schedule end time, or {@code null} for an open-ended schedule
    * @param scheduleTimezone the schedule timezone string (e.g. {@code "Asia/Tokyo"}), or {@code
-   *     null} to use the system default timezone
+   *     null} to use the global default timezone ({@code endpoint-gate.schedule.default-timezone}),
+   *     falling back to the system default timezone if no global default is configured
    * @param removeSchedule {@code true} to remove the schedule, or {@code null}/{@code false} to
    *     leave unchanged
    * @return a response reflecting the updated state of all gates

spring/actuator/src/main/java/net/brightroom/endpointgate/spring/actuator/endpoint/ReactiveEndpointGateEndpoint.java

@@ -110,7 +110,8 @@ public EndpointGateEndpointResponse gate(@Selector String gateId) {
    * @param scheduleStart the schedule start time, or {@code null} if only an end time is needed
    * @param scheduleEnd the schedule end time, or {@code null} for an open-ended schedule
    * @param scheduleTimezone the schedule timezone string (e.g. {@code "Asia/Tokyo"}), or {@code
-   *     null} to use the system default timezone
+   *     null} to use the global default timezone ({@code endpoint-gate.schedule.default-timezone}),
+   *     falling back to the system default timezone if no global default is configured
    * @param removeSchedule {@code true} to remove the schedule, or {@code null}/{@code false} to
    *     leave unchanged
    * @return a response reflecting the updated state of all gates

spring/actuator/src/test/java/net/brightroom/endpointgate/spring/actuator/endpoint/ReactiveEndpointGateEndpointTest.java

@@ -710,6 +710,57 @@ void gate_returnsUpdatedSchedule_afterUpdateGate() {
     assertThat(response.schedule().start()).isEqualTo(LocalDateTime.of(2026, 4, 1, 0, 0));
   }
 
+  @Test
+  void updateGate_usesDefaultScheduleTimezone_whenScheduleTimezoneNotSpecified() {
+    var provider = new MutableInMemoryReactiveEndpointGateProvider(Map.of("gate-a", true), false);
+    var scheduleProvider = new MutableInMemoryReactiveScheduleProvider(Map.of());
+    var endpoint =
+        new ReactiveEndpointGateEndpoint(
+            provider,
+            emptyRolloutProvider(),
+            emptyConditionProvider(),
+            scheduleProvider,
+            false,
+            ZoneId.of("Asia/Tokyo"),
+            eventPublisher,
+            clock);
+
+    endpoint.updateGate(
+        "gate-a", true, null, null, LocalDateTime.of(2026, 6, 1, 0, 0), null, null, null);
+
+    assertThat(scheduleProvider.getSchedule("gate-a").blockOptional())
+        .hasValueSatisfying(s -> assertThat(s.timezone()).isEqualTo(ZoneId.of("Asia/Tokyo")));
+  }
+
+  @Test
+  void updateGate_usesExplicitTimezone_overDefaultScheduleTimezone() {
+    var provider = new MutableInMemoryReactiveEndpointGateProvider(Map.of("gate-a", true), false);
+    var scheduleProvider = new MutableInMemoryReactiveScheduleProvider(Map.of());
+    var endpoint =
+        new ReactiveEndpointGateEndpoint(
+            provider,
+            emptyRolloutProvider(),
+            emptyConditionProvider(),
+            scheduleProvider,
+            false,
+            ZoneId.of("Asia/Tokyo"),
+            eventPublisher,
+            clock);
+
+    endpoint.updateGate(
+        "gate-a",
+        true,
+        null,
+        null,
+        LocalDateTime.of(2026, 6, 1, 0, 0),
+        null,
+        "America/New_York",
+        null);
+
+    assertThat(scheduleProvider.getSchedule("gate-a").blockOptional())
+        .hasValueSatisfying(s -> assertThat(s.timezone()).isEqualTo(ZoneId.of("America/New_York")));
+  }
+
   @Test
   void updateGate_throwsIllegalArgumentException_whenOnlyScheduleTimezoneProvided() {
     var provider = new MutableInMemoryReactiveEndpointGateProvider(Map.of("gate-a", true), false);

spring/core/src/main/java/net/brightroom/endpointgate/spring/core/properties/GlobalScheduleProperties.java

@@ -1,6 +1,7 @@
 package net.brightroom.endpointgate.spring.core.properties;
 
 import java.time.ZoneId;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Global schedule configuration properties.
@@ -23,7 +24,7 @@ public class GlobalScheduleProperties {
    *
    * @return the default timezone, or {@code null}
    */
-  public ZoneId defaultTimezone() {
+  public @Nullable ZoneId defaultTimezone() {
     return defaultTimezone;
   }
 

spring/core/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -51,7 +51,7 @@
     {
       "name": "endpoint-gate.gates.[*].schedule.timezone",
       "type": "java.time.ZoneId",
-      "description": "The timezone used to evaluate start and end times. If omitted, the system default timezone is used.",
+      "description": "The timezone used to evaluate start and end times. If omitted, the global default timezone (endpoint-gate.schedule.default-timezone) is used. If neither is set, the system default timezone is used.",
       "defaultValue": "system default"
     },
     {