Fix some compile errors ... std::optional now detects unused variables

Author: andreilitvin

src/app/clusters/valve-configuration-and-control-server/valve-configuration-and-control-server.cpp

@@ -311,8 +311,6 @@ CHIP_ERROR SetValveLevel(EndpointId ep, DataModel::Nullable<Percent> level, Data
 {
     Delegate * delegate     = GetDelegate(ep);
     Optional<Status> status = Optional<Status>::Missing();
-    DataModel::Nullable<Percent> openLevel;
-    DataModel::Nullable<uint64_t> autoCloseTime;
     CHIP_ERROR attribute_error = CHIP_IM_GLOBAL_STATUS(UnsupportedAttribute);
 
     if (HasFeature(ep, ValveConfigurationAndControl::Feature::kTimeSync))
@@ -328,6 +326,7 @@ CHIP_ERROR SetValveLevel(EndpointId ep, DataModel::Nullable<Percent> level, Data
             VerifyOrReturnError(UnixEpochToChipEpochMicros(utcTime.count(), chipEpochTime), CHIP_ERROR_INVALID_TIME);
 
             uint64_t time = openDuration.Value() * chip::kMicrosecondsPerSecond;
+            DataModel::Nullable<uint64_t> autoCloseTime;
             autoCloseTime.SetNonNull(chipEpochTime + time);
             VerifyOrReturnError(Status::Success == AutoCloseTime::Set(ep, autoCloseTime), attribute_error);
         }

src/app/data-model/Nullable.h

@@ -55,6 +55,7 @@ struct Nullable : protected std::optional<T>
     // NOTE: as we transition to std::optional, these should be removed
     T & Value() & { return value(); }
     const T & Value() const & { return value(); }
+    const T & ValueOr(const T & defaultValue) const { return value_or(defaultValue); }
     Nullable(NullOptionalType) : std::optional<T>(std::nullopt) {}
 
     // Some consumers need an easy way to determine our underlying type.