Polish nullability + something else

14 files changed, 86 insertions, 102 deletions

diff --git a/src/objective-c/GRPCClient/GRPCCall.h b/src/objective-c/GRPCClient/GRPCCall.h
index bde69f01c5..fcda4dc8ac 100644
--- a/src/objective-c/GRPCClient/GRPCCall.h
+++ b/src/objective-c/GRPCClient/GRPCCall.h
@@ -159,14 +159,14 @@ extern NSString *const kGRPCTrailersKey;
  * Issued when initial metadata is received from the server. The task must be scheduled onto the
  * dispatch queue in property \a dispatchQueue.
  */
-- (void)receivedInitialMetadata:(NSDictionary *_Nullable)initialMetadata;
+- (void)receivedInitialMetadata:(nullable NSDictionary *)initialMetadata;
 
 /**
  * Issued when a message is received from the server. The message is the raw data received from the
  * server, with decompression and without proto deserialization. The task must be scheduled onto the
  * dispatch queue in property \a dispatchQueue.
  */
-- (void)receivedRawMessage:(NSData *_Nullable)message;
+- (void)receivedRawMessage:(nullable NSData *)message;
 
 /**
  * Issued when a call finished. If the call finished successfully, \a error is nil and \a
@@ -175,8 +175,8 @@ extern NSString *const kGRPCTrailersKey;
  * error descriptions. The task must be scheduled onto the dispatch queue in property
  * \a dispatchQueue.
  */
-- (void)closedWithTrailingMetadata:(NSDictionary *_Nullable)trailingMetadata
-                             error:(NSError *_Nullable)error;
+- (void)closedWithTrailingMetadata:(nullable NSDictionary *)trailingMetadata
+                             error:(nullable NSError *)error;
 
 @required
 
@@ -234,7 +234,7 @@ extern NSString *const kGRPCTrailersKey;
  */
 - (instancetype)initWithRequestOptions:(GRPCRequestOptions *)requestOptions
                        responseHandler:(id<GRPCResponseHandler>)responseHandler
-                           callOptions:(GRPCCallOptions *_Nullable)callOptions
+                           callOptions:(nullable GRPCCallOptions *)callOptions
     NS_DESIGNATED_INITIALIZER;
 /**
  * Convenience initializer for a call that uses default call options (see GRPCCallOptions.m for
@@ -342,9 +342,9 @@ NS_ASSUME_NONNULL_END
  * host parameter should not contain the scheme (http:// or https://), only the name or IP addr
  * and the port number, for example @"localhost:5050".
  */
-- (instancetype _Null_unspecified)initWithHost:(NSString *_Null_unspecified)host
-                                          path:(NSString *_Null_unspecified)path
-                                requestsWriter:(GRXWriter *_Null_unspecified)requestWriter;
+- (null_unspecified instancetype)initWithHost:(null_unspecified NSString *)host
+                                          path:(null_unspecified NSString *)path
+                                requestsWriter:(null_unspecified GRXWriter *)requestWriter;
 
 /**
  * Finishes the request side of this call, notifies the server that the RPC should be cancelled, and
@@ -356,11 +356,11 @@ NS_ASSUME_NONNULL_END
  * The following methods are deprecated.
  */
 + (void)setCallSafety:(GRPCCallSafety)callSafety
-                 host:(NSString *_Null_unspecified)host
-                 path:(NSString *_Null_unspecified)path;
+                 host:(null_unspecified NSString *)host
+                 path:(null_unspecified NSString *)path;
 @property(null_unspecified, atomic, copy, readwrite) NSString *serverName;
 @property NSTimeInterval timeout;
-- (void)setResponseDispatchQueue:(dispatch_queue_t _Null_unspecified)queue;
+- (void)setResponseDispatchQueue:(null_unspecified dispatch_queue_t)queue;
 
 @end
 
@@ -371,11 +371,11 @@ DEPRECATED_MSG_ATTRIBUTE("Use NSDictionary or NSMutableDictionary instead.")
 @protocol GRPCRequestHeaders<NSObject>
 @property(nonatomic, readonly) NSUInteger count;
 
-- (id _Null_unspecified)objectForKeyedSubscript:(id _Null_unspecified)key;
-- (void)setObject:(id _Null_unspecified)obj forKeyedSubscript:(id _Null_unspecified)key;
+- (null_unspecified id)objectForKeyedSubscript:(null_unspecified id)key;
+- (void)setObject:(null_unspecified id)obj forKeyedSubscript:(null_unspecified id)key;
 
 - (void)removeAllObjects;
-- (void)removeObjectForKey:(id _Null_unspecified)key;
+- (void)removeObjectForKey:(null_unspecified id)key;
 @end
 
 #pragma clang diagnostic push
diff --git a/src/objective-c/GRPCClient/GRPCCall.m b/src/objective-c/GRPCClient/GRPCCall.m
index 788afeb6c3..68b51d8c84 100644
--- a/src/objective-c/GRPCClient/GRPCCall.m
+++ b/src/objective-c/GRPCClient/GRPCCall.m
@@ -114,7 +114,7 @@ const char *kCFStreamVarName = "grpc_cfstream";
 
 - (instancetype)initWithRequestOptions:(GRPCRequestOptions *)requestOptions
                        responseHandler:(id<GRPCResponseHandler>)responseHandler
-                           callOptions:(GRPCCallOptions *_Nullable)callOptions {
+                           callOptions:(GRPCCallOptions *)callOptions {
   NSAssert(requestOptions.host.length != 0 && requestOptions.path.length != 0,
              @"Neither host nor path can be nil.");
   NSAssert(requestOptions.safety <= GRPCCallSafetyCacheableRequest,
@@ -134,7 +134,7 @@ const char *kCFStreamVarName = "grpc_cfstream";
     if (@available(iOS 8.0, *)) {
       _dispatchQueue = dispatch_queue_create(
           NULL,
-          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, -1));
+          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, 0));
     } else {
       // Fallback on earlier versions
       _dispatchQueue = dispatch_queue_create(NULL, DISPATCH_QUEUE_SERIAL);
diff --git a/src/objective-c/GRPCClient/GRPCCallOptions.h b/src/objective-c/GRPCClient/GRPCCallOptions.h
index bb8a1d251a..61d8564286 100644
--- a/src/objective-c/GRPCClient/GRPCCallOptions.h
+++ b/src/objective-c/GRPCClient/GRPCCallOptions.h
@@ -78,7 +78,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  *       :authority header field of the call and performs an extra check that server's certificate
  *       matches the :authority header.
  */
-@property(copy, readonly) NSString *serverAuthority;
+@property(copy, readonly, nullable) NSString *serverAuthority;
 
 /**
  * The timeout for the RPC call in seconds. If set to 0, the call will not timeout. If set to
@@ -94,18 +94,18 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * request's "authorization" header field. This parameter should not be used simultaneously with
  * \a authTokenProvider.
  */
-@property(copy, readonly) NSString *oauth2AccessToken;
+@property(copy, readonly, nullable) NSString *oauth2AccessToken;
 
 /**
  * The interface to get the OAuth2 access token string. gRPC will attempt to acquire token when
  * initiating the call. This parameter should not be used simultaneously with \a oauth2AccessToken.
  */
-@property(readonly) id<GRPCAuthorizationProtocol> authTokenProvider;
+@property(readonly, nullable) id<GRPCAuthorizationProtocol> authTokenProvider;
 
 /**
  * Initial metadata key-value pairs that should be included in the request.
  */
-@property(copy, readonly) NSDictionary *initialMetadata;
+@property(copy, readonly, nullable) NSDictionary *initialMetadata;
 
 // Channel parameters; take into account of channel signature.
 
@@ -113,7 +113,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * Custom string that is prefixed to a request's user-agent header field before gRPC's internal
  * user-agent string.
  */
-@property(copy, readonly) NSString *userAgentPrefix;
+@property(copy, readonly, nullable) NSString *userAgentPrefix;
 
 /**
  * The size limit for the response received from server. If it is exceeded, an error with status
@@ -152,7 +152,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * Specify channel args to be used for this call. For a list of channel args available, see
  * grpc/grpc_types.h
  */
-@property(copy, readonly) NSDictionary *additionalChannelArgs;
+@property(copy, readonly, nullable) NSDictionary *additionalChannelArgs;
 
 // Parameters for SSL authentication.
 
@@ -160,17 +160,17 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * PEM format root certifications that is trusted. If set to nil, gRPC uses a list of default
  * root certificates.
  */
-@property(copy, readonly) NSString *PEMRootCertificates;
+@property(copy, readonly, nullable) NSString *PEMRootCertificates;
 
 /**
  * PEM format private key for client authentication, if required by the server.
  */
-@property(copy, readonly) NSString *PEMPrivateKey;
+@property(copy, readonly, nullable) NSString *PEMPrivateKey;
 
 /**
  * PEM format certificate chain for client authentication, if required by the server.
  */
-@property(copy, readonly) NSString *PEMCertChain;
+@property(copy, readonly, nullable) NSString *PEMCertChain;
 
 /**
  * Select the transport type to be used for this call.
@@ -180,13 +180,13 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
 /**
  * Override the hostname during the TLS hostname validation process.
  */
-@property(copy, readonly) NSString *hostNameOverride;
+@property(copy, readonly, nullable) NSString *hostNameOverride;
 
 /**
  * A string that specify the domain where channel is being cached. Channels with different domains
  * will not get cached to the same connection.
  */
-@property(copy, readonly) NSString *channelPoolDomain;
+@property(copy, readonly, nullable) NSString *channelPoolDomain;
 
 /**
  * Channel id allows control of channel caching within a channelPoolDomain. A call with a unique
@@ -199,7 +199,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
 /**
  * Return if the channel options are equal to another object.
  */
-- (BOOL)hasChannelOptionsEqualTo:(GRPCCallOptions *)callOptions;
+- (BOOL)hasChannelOptionsEqualTo:(nonnull GRPCCallOptions *)callOptions;
 
 /**
  * Hash for channel options.
@@ -219,7 +219,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  *       :authority header field of the call and performs an extra check that server's certificate
  *       matches the :authority header.
  */
-@property(copy, readwrite) NSString *serverAuthority;
+@property(copy, readwrite, nullable) NSString *serverAuthority;
 
 /**
  * The timeout for the RPC call in seconds. If set to 0, the call will not timeout. If set to
@@ -236,18 +236,18 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * request's "authorization" header field. This parameter should not be used simultaneously with
  * \a authTokenProvider.
  */
-@property(copy, readwrite) NSString *oauth2AccessToken;
+@property(copy, readwrite, nullable) NSString *oauth2AccessToken;
 
 /**
  * The interface to get the OAuth2 access token string. gRPC will attempt to acquire token when
  * initiating the call. This parameter should not be used simultaneously with \a oauth2AccessToken.
  */
-@property(readwrite) id<GRPCAuthorizationProtocol> authTokenProvider;
+@property(readwrite, nullable) id<GRPCAuthorizationProtocol> authTokenProvider;
 
 /**
  * Initial metadata key-value pairs that should be included in the request.
  */
-@property(copy, readwrite) NSDictionary *initialMetadata;
+@property(copy, readwrite, nullable) NSDictionary *initialMetadata;
 
 // Channel parameters; take into account of channel signature.
 
@@ -255,7 +255,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * Custom string that is prefixed to a request's user-agent header field before gRPC's internal
  * user-agent string.
  */
-@property(copy, readwrite) NSString *userAgentPrefix;
+@property(copy, readwrite, nullable) NSString *userAgentPrefix;
 
 /**
  * The size limit for the response received from server. If it is exceeded, an error with status
@@ -296,7 +296,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * Specify channel args to be used for this call. For a list of channel args available, see
  * grpc/grpc_types.h
  */
-@property(copy, readwrite) NSDictionary *additionalChannelArgs;
+@property(copy, readwrite, nullable) NSDictionary *additionalChannelArgs;
 
 // Parameters for SSL authentication.
 
@@ -304,17 +304,17 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * PEM format root certifications that is trusted. If set to nil, gRPC uses a list of default
  * root certificates.
  */
-@property(copy, readwrite) NSString *PEMRootCertificates;
+@property(copy, readwrite, nullable) NSString *PEMRootCertificates;
 
 /**
  * PEM format private key for client authentication, if required by the server.
  */
-@property(copy, readwrite) NSString *PEMPrivateKey;
+@property(copy, readwrite, nullable) NSString *PEMPrivateKey;
 
 /**
  * PEM format certificate chain for client authentication, if required by the server.
  */
-@property(copy, readwrite) NSString *PEMCertChain;
+@property(copy, readwrite, nullable) NSString *PEMCertChain;
 
 /**
  * Select the transport type to be used for this call.
@@ -324,7 +324,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
 /**
  * Override the hostname during the TLS hostname validation process.
  */
-@property(copy, readwrite) NSString *hostNameOverride;
+@property(copy, readwrite, nullable) NSString *hostNameOverride;
 
 /**
  * A string that specify the domain where channel is being cached. Channels with different domains
@@ -332,7 +332,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * domain 'io.grpc.example' so that its calls do not reuse the channel created by other modules in
  * the same process.
  */
-@property(copy, readwrite) NSString *channelPoolDomain;
+@property(copy, readwrite, nullable) NSString *channelPoolDomain;
 
 /**
  * Channel id allows a call to force creating a new channel (connection) rather than using a cached
diff --git a/src/objective-c/GRPCClient/private/GRPCChannel.h b/src/objective-c/GRPCClient/private/GRPCChannel.h
index 32e68bb262..4dbe0c276c 100644
--- a/src/objective-c/GRPCClient/private/GRPCChannel.h
+++ b/src/objective-c/GRPCClient/private/GRPCChannel.h
@@ -85,7 +85,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (nullable grpc_call *)unmanagedCallWithPath:(NSString *)path
                               completionQueue:(GRPCCompletionQueue *)queue
                                   callOptions:(GRPCCallOptions *)callOptions
-                                 disconnected:(BOOL *_Nullable)disconnected;
+                                 disconnected:(nullable BOOL *)disconnected;
 
 /**
  * Unref the channel when a call is done. It also decreases the channel's refcount. If the refcount
diff --git a/src/objective-c/GRPCClient/private/GRPCChannel.m b/src/objective-c/GRPCClient/private/GRPCChannel.m
index ab084fba48..de3302598e 100644
--- a/src/objective-c/GRPCClient/private/GRPCChannel.m
+++ b/src/objective-c/GRPCClient/private/GRPCChannel.m
@@ -39,7 +39,7 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
 
 @implementation GRPCChannelConfiguration
 
-- (nullable instancetype)initWithHost:(NSString *)host callOptions:(GRPCCallOptions *)callOptions {
+- (instancetype)initWithHost:(NSString *)host callOptions:(GRPCCallOptions *)callOptions {
   NSAssert(host.length, @"Host must not be empty.");
   NSAssert(callOptions != nil, @"callOptions must not be empty.");
   if ((self = [super init])) {
@@ -143,7 +143,7 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
   return args;
 }
 
-- (nonnull id)copyWithZone:(nullable NSZone *)zone {
+- (id)copyWithZone:(NSZone *)zone {
   GRPCChannelConfiguration *newConfig =
       [[GRPCChannelConfiguration alloc] initWithHost:_host callOptions:_callOptions];
 
@@ -184,13 +184,13 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
 }
 @synthesize disconnected = _disconnected;
 
-- (nullable instancetype)initWithChannelConfiguration:
+- (instancetype)initWithChannelConfiguration:
     (GRPCChannelConfiguration *)channelConfiguration {
   return [self initWithChannelConfiguration:channelConfiguration
                                destroyDelay:kDefaultChannelDestroyDelay];
 }
 
-- (nullable instancetype)initWithChannelConfiguration:
+- (instancetype)initWithChannelConfiguration:
                              (GRPCChannelConfiguration *)channelConfiguration
                                          destroyDelay:(NSTimeInterval)destroyDelay {
   NSAssert(channelConfiguration != nil,
@@ -201,7 +201,7 @@ static const NSTimeInterval kDefaultChannelDestroyDelay = 30;
     if (@available(iOS 8.0, *)) {
       _dispatchQueue = dispatch_queue_create(
           NULL,
-          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, -1));
+          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, 0));
     } else {
       _dispatchQueue = dispatch_queue_create(NULL, DISPATCH_QUEUE_SERIAL);
     }
diff --git a/src/objective-c/GRPCClient/private/GRPCChannelFactory.h b/src/objective-c/GRPCClient/private/GRPCChannelFactory.h
index 3a3500fc95..a934e966e9 100644
--- a/src/objective-c/GRPCClient/private/GRPCChannelFactory.h
+++ b/src/objective-c/GRPCClient/private/GRPCChannelFactory.h
@@ -26,8 +26,8 @@ NS_ASSUME_NONNULL_BEGIN
 @protocol GRPCChannelFactory
 
 /** Create a channel with specific channel args to a specific host. */
-- (grpc_channel *_Nullable)createChannelWithHost:(NSString *)host
-                                     channelArgs:(NSDictionary *_Nullable)args;
+- (nullable grpc_channel *)createChannelWithHost:(NSString *)host
+                                     channelArgs:(nullable NSDictionary *)args;
 
 @end
 
diff --git a/src/objective-c/GRPCClient/private/GRPCChannelPool.m b/src/objective-c/GRPCClient/private/GRPCChannelPool.m
index 6745010bd4..72554ca6dc 100644
--- a/src/objective-c/GRPCClient/private/GRPCChannelPool.m
+++ b/src/objective-c/GRPCClient/private/GRPCChannelPool.m
@@ -41,7 +41,7 @@ static dispatch_once_t gInitChannelPool;
   NSMutableDictionary<GRPCChannelConfiguration *, GRPCChannel *> *_channelPool;
 }
 
-+ (nullable instancetype)sharedInstance {
++ (instancetype)sharedInstance {
   dispatch_once(&gInitChannelPool, ^{
     gChannelPool = [[GRPCChannelPool alloc] init];
     NSAssert(gChannelPool != nil, @"Cannot initialize global channel pool.");
diff --git a/src/objective-c/GRPCClient/private/GRPCConnectivityMonitor.m b/src/objective-c/GRPCClient/private/GRPCConnectivityMonitor.m
index a36788b35a..bb8618ff33 100644
--- a/src/objective-c/GRPCClient/private/GRPCConnectivityMonitor.m
+++ b/src/objective-c/GRPCClient/private/GRPCConnectivityMonitor.m
@@ -76,14 +76,14 @@ static void ReachabilityCallback(SCNetworkReachabilityRef target, SCNetworkReach
   }
 }
 
-+ (void)registerObserver:(_Nonnull id)observer selector:(SEL)selector {
++ (void)registerObserver:(id)observer selector:(SEL)selector {
   [[NSNotificationCenter defaultCenter] addObserver:observer
                                            selector:selector
                                                name:kGRPCConnectivityNotification
                                              object:nil];
 }
 
-+ (void)unregisterObserver:(_Nonnull id)observer {
++ (void)unregisterObserver:(id)observer {
   [[NSNotificationCenter defaultCenter] removeObserver:observer];
 }
 
diff --git a/src/objective-c/GRPCClient/private/GRPCCronetChannelFactory.m b/src/objective-c/GRPCClient/private/GRPCCronetChannelFactory.m
index 781881d211..74ea9723b3 100644
--- a/src/objective-c/GRPCClient/private/GRPCCronetChannelFactory.m
+++ b/src/objective-c/GRPCClient/private/GRPCCronetChannelFactory.m
@@ -26,13 +26,11 @@
 #import <Cronet/Cronet.h>
 #include <grpc/grpc_cronet.h>
 
-NS_ASSUME_NONNULL_BEGIN
-
 @implementation GRPCCronetChannelFactory {
   stream_engine *_cronetEngine;
 }
 
-+ (instancetype _Nullable)sharedInstance {
++ (instancetype)sharedInstance {
   static GRPCCronetChannelFactory *instance;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
@@ -41,7 +39,7 @@ NS_ASSUME_NONNULL_BEGIN
   return instance;
 }
 
-- (instancetype _Nullable)initWithEngine:(stream_engine *)engine {
+- (instancetype)initWithEngine:(stream_engine *)engine {
   if (!engine) {
     [NSException raise:NSInvalidArgumentException format:@"Cronet engine is NULL. Set it first."];
     return nil;
@@ -52,8 +50,8 @@ NS_ASSUME_NONNULL_BEGIN
   return self;
 }
 
-- (grpc_channel *_Nullable)createChannelWithHost:(NSString *)host
-                                     channelArgs:(NSDictionary *_Nullable)args {
+- (grpc_channel *)createChannelWithHost:(NSString *)host
+                                     channelArgs:(NSDictionary *)args {
   grpc_channel_args *channelArgs = GRPCBuildChannelArgs(args);
   grpc_channel *unmanagedChannel =
       grpc_cronet_secure_channel_create(_cronetEngine, host.UTF8String, channelArgs, NULL);
@@ -63,22 +61,18 @@ NS_ASSUME_NONNULL_BEGIN
 
 @end
 
-NS_ASSUME_NONNULL_END
-
 #else
 
-NS_ASSUME_NONNULL_BEGIN
-
 @implementation GRPCCronetChannelFactory
 
-+ (instancetype _Nullable)sharedInstance {
++ (instancetype)sharedInstance {
   [NSException raise:NSInvalidArgumentException
               format:@"Must enable macro GRPC_COMPILE_WITH_CRONET to build Cronet channel."];
   return nil;
 }
 
-- (grpc_channel *_Nullable)createChannelWithHost:(NSString *)host
-                                     channelArgs:(NSDictionary *_Nullable)args {
+- (grpc_channel *)createChannelWithHost:(NSString *)host
+                                     channelArgs:(NSDictionary *)args {
   [NSException raise:NSInvalidArgumentException
               format:@"Must enable macro GRPC_COMPILE_WITH_CRONET to build Cronet channel."];
   return NULL;
@@ -86,6 +80,4 @@ NS_ASSUME_NONNULL_BEGIN
 
 @end
 
-NS_ASSUME_NONNULL_END
-
 #endif
diff --git a/src/objective-c/GRPCClient/private/GRPCInsecureChannelFactory.m b/src/objective-c/GRPCClient/private/GRPCInsecureChannelFactory.m
index 9969887712..3e9ebe7ae0 100644
--- a/src/objective-c/GRPCClient/private/GRPCInsecureChannelFactory.m
+++ b/src/objective-c/GRPCClient/private/GRPCInsecureChannelFactory.m
@@ -21,11 +21,9 @@
 #import "ChannelArgsUtil.h"
 #import "GRPCChannel.h"
 
-NS_ASSUME_NONNULL_BEGIN
-
 @implementation GRPCInsecureChannelFactory
 
-+ (instancetype _Nullable)sharedInstance {
++ (instancetype)sharedInstance {
   static GRPCInsecureChannelFactory *instance;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
@@ -34,8 +32,8 @@ NS_ASSUME_NONNULL_BEGIN
   return instance;
 }
 
-- (grpc_channel *_Nullable)createChannelWithHost:(NSString *)host
-                                     channelArgs:(NSDictionary *_Nullable)args {
+- (grpc_channel *)createChannelWithHost:(NSString *)host
+                                     channelArgs:(NSDictionary *)args {
   grpc_channel_args *coreChannelArgs = GRPCBuildChannelArgs([args copy]);
   grpc_channel *unmanagedChannel =
       grpc_insecure_channel_create(host.UTF8String, coreChannelArgs, NULL);
@@ -44,5 +42,3 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 @end
-
-NS_ASSUME_NONNULL_END
diff --git a/src/objective-c/GRPCClient/private/GRPCSecureChannelFactory.m b/src/objective-c/GRPCClient/private/GRPCSecureChannelFactory.m
index f5e7a2b9e2..2e7f1a0dbe 100644
--- a/src/objective-c/GRPCClient/private/GRPCSecureChannelFactory.m
+++ b/src/objective-c/GRPCClient/private/GRPCSecureChannelFactory.m
@@ -24,15 +24,13 @@
 #import "GRPCChannel.h"
 #import "utilities.h"
 
-NS_ASSUME_NONNULL_BEGIN
-
 @implementation GRPCSecureChannelFactory {
   grpc_channel_credentials *_channelCreds;
 }
 
-+ (instancetype _Nullable)factoryWithPEMRootCertificates:(NSString *_Nullable)rootCerts
-                                              privateKey:(NSString *_Nullable)privateKey
-                                               certChain:(NSString *_Nullable)certChain
++ (instancetype)factoryWithPEMRootCertificates:(NSString *)rootCerts
+                                              privateKey:(NSString *)privateKey
+                                               certChain:(NSString *)certChain
                                                    error:(NSError **)errorPtr {
   return [[self alloc] initWithPEMRootCerts:rootCerts
                                  privateKey:privateKey
@@ -40,7 +38,7 @@ NS_ASSUME_NONNULL_BEGIN
                                       error:errorPtr];
 }
 
-- (NSData *_Nullable)nullTerminatedDataWithString:(NSString *_Nullable)string {
+- (NSData *)nullTerminatedDataWithString:(NSString *)string {
   // dataUsingEncoding: does not return a null-terminated string.
   NSData *data = [string dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
   if (data == nil) {
@@ -51,9 +49,9 @@ NS_ASSUME_NONNULL_BEGIN
   return nullTerminated;
 }
 
-- (instancetype _Nullable)initWithPEMRootCerts:(NSString *_Nullable)rootCerts
-                                    privateKey:(NSString *_Nullable)privateKey
-                                     certChain:(NSString *_Nullable)certChain
+- (instancetype)initWithPEMRootCerts:(NSString *)rootCerts
+                                    privateKey:(NSString *)privateKey
+                                     certChain:(NSString *)certChain
                                          error:(NSError **)errorPtr {
   static NSData *defaultRootsASCII;
   static NSError *defaultRootsError;
@@ -117,8 +115,8 @@ NS_ASSUME_NONNULL_BEGIN
   return self;
 }
 
-- (grpc_channel *_Nullable)createChannelWithHost:(NSString *)host
-                                     channelArgs:(NSDictionary *_Nullable)args {
+- (grpc_channel *)createChannelWithHost:(NSString *)host
+                                     channelArgs:(NSDictionary *)args {
   grpc_channel_args *coreChannelArgs = GRPCBuildChannelArgs([args copy]);
   grpc_channel *unmanagedChannel =
       grpc_secure_channel_create(_channelCreds, host.UTF8String, coreChannelArgs, NULL);
@@ -133,5 +131,3 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 @end
-
-NS_ASSUME_NONNULL_END
diff --git a/src/objective-c/ProtoRPC/ProtoRPC.h b/src/objective-c/ProtoRPC/ProtoRPC.h
index b0f4ced99e..dc776368a8 100644
--- a/src/objective-c/ProtoRPC/ProtoRPC.h
+++ b/src/objective-c/ProtoRPC/ProtoRPC.h
@@ -33,13 +33,13 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  * Issued when initial metadata is received from the server. The task must be scheduled onto the
  * dispatch queue in property \a dispatchQueue. */
-- (void)receivedInitialMetadata:(NSDictionary *_Nullable)initialMetadata;
+- (void)receivedInitialMetadata:(nullable NSDictionary *)initialMetadata;
 
 /**
  * Issued when a message is received from the server. The message is the deserialized proto object.
  * The task must be scheduled onto the dispatch queue in property \a dispatchQueue.
  */
-- (void)receivedProtoMessage:(GPBMessage *_Nullable)message;
+- (void)receivedProtoMessage:(nullable GPBMessage *)message;
 
 /**
  * Issued when a call finished. If the call finished successfully, \a error is nil and \a
@@ -48,8 +48,8 @@ NS_ASSUME_NONNULL_BEGIN
  * error descriptions. The task must be scheduled onto the dispatch queue in property
  * \a dispatchQueue.
  */
-- (void)closedWithTrailingMetadata:(NSDictionary *_Nullable)trailingMetadata
-                             error:(NSError *_Nullable)error;
+- (void)closedWithTrailingMetadata:(nullable NSDictionary *)trailingMetadata
+                             error:(nullable NSError *)error;
 
 @required
 
@@ -75,7 +75,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (instancetype)initWithRequestOptions:(GRPCRequestOptions *)requestOptions
                                message:(GPBMessage *)message
                        responseHandler:(id<GRPCProtoResponseHandler>)handler
-                           callOptions:(GRPCCallOptions *_Nullable)callOptions
+                           callOptions:(nullable GRPCCallOptions *)callOptions
                          responseClass:(Class)responseClass NS_DESIGNATED_INITIALIZER;
 
 /**
@@ -100,7 +100,7 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (instancetype)initWithRequestOptions:(GRPCRequestOptions *)requestOptions
                        responseHandler:(id<GRPCProtoResponseHandler>)handler
-                           callOptions:(GRPCCallOptions *_Nullable)callOptions
+                           callOptions:(nullable GRPCCallOptions *)callOptions
                          responseClass:(Class)responseClass NS_DESIGNATED_INITIALIZER;
 
 /**
diff --git a/src/objective-c/ProtoRPC/ProtoRPC.m b/src/objective-c/ProtoRPC/ProtoRPC.m
index 34891e8953..f99da45fef 100644
--- a/src/objective-c/ProtoRPC/ProtoRPC.m
+++ b/src/objective-c/ProtoRPC/ProtoRPC.m
@@ -52,7 +52,7 @@ static NSError *ErrorForBadProto(id proto, Class expectedClass, NSError *parsing
 - (instancetype)initWithRequestOptions:(GRPCRequestOptions *)requestOptions
                                message:(GPBMessage *)message
                        responseHandler:(id<GRPCProtoResponseHandler>)handler
-                           callOptions:(GRPCCallOptions *_Nullable)callOptions
+                           callOptions:(GRPCCallOptions *)callOptions
                          responseClass:(Class)responseClass {
   if ((self = [super init])) {
     _call = [[GRPCStreamingProtoCall alloc] initWithRequestOptions:requestOptions
@@ -88,7 +88,7 @@ static NSError *ErrorForBadProto(id proto, Class expectedClass, NSError *parsing
 
 - (instancetype)initWithRequestOptions:(GRPCRequestOptions *)requestOptions
                        responseHandler:(id<GRPCProtoResponseHandler>)handler
-                           callOptions:(GRPCCallOptions *_Nullable)callOptions
+                           callOptions:(GRPCCallOptions *)callOptions
                          responseClass:(Class)responseClass {
   if (requestOptions.host.length == 0 || requestOptions.path.length == 0) {
     [NSException raise:NSInvalidArgumentException format:@"Neither host nor path can be nil."];
@@ -108,7 +108,7 @@ static NSError *ErrorForBadProto(id proto, Class expectedClass, NSError *parsing
     if (@available(iOS 8.0, *)) {
       _dispatchQueue = dispatch_queue_create(
           NULL,
-          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, -1));
+          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, 0));
     } else {
       _dispatchQueue = dispatch_queue_create(nil, DISPATCH_QUEUE_SERIAL);
     }
@@ -171,7 +171,7 @@ static NSError *ErrorForBadProto(id proto, Class expectedClass, NSError *parsing
   });
 }
 
-- (void)receivedInitialMetadata:(NSDictionary *_Nullable)initialMetadata {
+- (void)receivedInitialMetadata:(NSDictionary *)initialMetadata {
   dispatch_async(_dispatchQueue, ^{
     if (initialMetadata != nil && [self->_handler respondsToSelector:@selector(initialMetadata:)]) {
       [self->_handler receivedInitialMetadata:initialMetadata];
@@ -179,7 +179,7 @@ static NSError *ErrorForBadProto(id proto, Class expectedClass, NSError *parsing
   });
 }
 
-- (void)receivedRawMessage:(NSData *_Nullable)message {
+- (void)receivedRawMessage:(NSData *)message {
   dispatch_async(_dispatchQueue, ^{
     if (self->_handler && message != nil) {
       NSError *error = nil;
@@ -202,8 +202,8 @@ static NSError *ErrorForBadProto(id proto, Class expectedClass, NSError *parsing
   });
 }
 
-- (void)closedWithTrailingMetadata:(NSDictionary *_Nullable)trailingMetadata
-                             error:(NSError *_Nullable)error {
+- (void)closedWithTrailingMetadata:(NSDictionary *)trailingMetadata
+                             error:(NSError *)error {
   dispatch_async(_dispatchQueue, ^{
     if ([self->_handler respondsToSelector:@selector(closedWithTrailingMetadata:error:)]) {
       [self->_handler closedWithTrailingMetadata:trailingMetadata error:error];
diff --git a/src/objective-c/tests/InteropTests.m b/src/objective-c/tests/InteropTests.m
index c42718f15e..dcc8f1b589 100644
--- a/src/objective-c/tests/InteropTests.m
+++ b/src/objective-c/tests/InteropTests.m
@@ -102,7 +102,7 @@ BOOL isRemoteInteropTest(NSString *host) {
   return self;
 }
 
-- (void)receivedInitialMetadata:(NSDictionary *_Nullable)initialMetadata {
+- (void)receivedInitialMetadata:(NSDictionary *)initialMetadata {
   dispatch_async(_dispatchQueue, ^{
     if (_initialMetadataCallback) {
       _initialMetadataCallback(initialMetadata);
@@ -110,7 +110,7 @@ BOOL isRemoteInteropTest(NSString *host) {
   });
 }
 
-- (void)receivedProtoMessage:(GPBMessage *_Nullable)message {
+- (void)receivedProtoMessage:(GPBMessage *)message {
   dispatch_async(_dispatchQueue, ^{
     if (_messageCallback) {
       _messageCallback(message);
@@ -118,8 +118,8 @@ BOOL isRemoteInteropTest(NSString *host) {
   });
 }
 
-- (void)closedWithTrailingMetadata:(NSDictionary *_Nullable)trailingMetadata
-                             error:(NSError *_Nullable)error {
+- (void)closedWithTrailingMetadata:(NSDictionary *)trailingMetadata
+                             error:(NSError *)error {
   dispatch_async(_dispatchQueue, ^{
     if (_closeCallback) {
       _closeCallback(trailingMetadata, error);