Mark return types nullable in MTRDevice_XPC when nil can be returned.

Author: bzbarsky-apple

src/darwin/Framework/CHIP/MTRDevice_XPC.mm

@@ -163,10 +163,10 @@ - (oneway void)deviceConfigurationChanged:(NSNumber *)nodeID
 
 MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(state, MTRDeviceState, MTRDeviceStateUnknown, getStateWithReply)
 MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(deviceCachePrimed, BOOL, NO, getDeviceCachePrimedWithReply)
-MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(estimatedStartTime, NSDate *, nil, getEstimatedStartTimeWithReply)
-MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(estimatedSubscriptionLatency, NSNumber *, nil, getEstimatedSubscriptionLatencyWithReply)
+MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(estimatedStartTime, NSDate * _Nullable, nil, getEstimatedStartTimeWithReply)
+MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(estimatedSubscriptionLatency, NSNumber * _Nullable, nil, getEstimatedSubscriptionLatencyWithReply)
 
-typedef NSDictionary<NSString *, id> * readAttributeResponseType;
+typedef NSDictionary<NSString *, id> * _Nullable readAttributeResponseType;
 MTR_DEVICE_COMPLEX_REMOTE_XPC_GETTER(readAttributeWithEndpointID
                                      : (NSNumber *) endpointID clusterID
                                      : (NSNumber *) clusterID attributeID
@@ -223,7 +223,7 @@ - (void)invokeCommandWithEndpointID:(NSNumber *)endpointID
 // Not Supported via XPC
 //- (oneway void)deviceController:(NSUUID *)controller nodeID:(NSNumber *)nodeID openCommissioningWindowWithSetupPasscode:(NSNumber *)setupPasscode discriminator:(NSNumber *)discriminator duration:(NSNumber *)duration completion:(MTRDeviceOpenCommissioningWindowHandler)completion;
 
-MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(clientDataKeys, NSArray *, nil, getClientDataKeysWithReply)
+MTR_DEVICE_SIMPLE_REMOTE_XPC_GETTER(clientDataKeys, NSArray * _Nullable, nil, getClientDataKeysWithReply)
 MTR_DEVICE_COMPLEX_REMOTE_XPC_GETTER(clientDataForKey
                                      : (NSString *) key, id<NSSecureCoding> _Nullable, nil, clientDataForKey
                                      : key withReply)