Fix nullability (#4551)

AFNetworking/AFHTTPSessionManager.h

@@ -271,14 +271,14 @@ NS_ASSUME_NONNULL_BEGIN
 
  @see -dataTaskWithRequest:uploadProgress:downloadProgress:completionHandler:
  */
-- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
-                                       URLString:(NSString *)URLString
-                                      parameters:(nullable id)parameters
-                                         headers:(nullable NSDictionary <NSString *, NSString *> *)headers
-                                  uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
-                                downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
-                                         success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
-                                         failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;
+- (nullable NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
+                                                URLString:(NSString *)URLString
+                                               parameters:(nullable id)parameters
+                                                  headers:(nullable NSDictionary <NSString *, NSString *> *)headers
+                                           uploadProgress:(nullable void (^)(NSProgress *uploadProgress))uploadProgress
+                                         downloadProgress:(nullable void (^)(NSProgress *downloadProgress))downloadProgress
+                                                  success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
+                                                  failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;
 
 @end
 

AFNetworking/AFURLRequestSerialization.h

@@ -216,7 +216,7 @@ forHTTPHeaderField:(NSString *)field;
 
  @param block A block that defines a process of encoding parameters into a query string. This block returns the query string and takes three arguments: the request, the parameters to encode, and the error that occurred when attempting to encode parameters for the given request.
  */
-- (void)setQueryStringSerializationWithBlock:(nullable NSString * (^)(NSURLRequest *request, id parameters, NSError * __autoreleasing *error))block;
+- (void)setQueryStringSerializationWithBlock:(nullable NSString * _Nullable (^)(NSURLRequest *request, id parameters, NSError * __autoreleasing *error))block;
 
 ///-------------------------------
 /// @name Creating Request Objects
@@ -234,10 +234,10 @@ forHTTPHeaderField:(NSString *)field;
 
  @return An `NSMutableURLRequest` object.
  */
-- (NSMutableURLRequest *)requestWithMethod:(NSString *)method
-                                 URLString:(NSString *)URLString
-                                parameters:(nullable id)parameters
-                                     error:(NSError * _Nullable __autoreleasing *)error;
+- (nullable NSMutableURLRequest *)requestWithMethod:(NSString *)method
+                                          URLString:(NSString *)URLString
+                                         parameters:(nullable id)parameters
+                                              error:(NSError * _Nullable __autoreleasing *)error;
 
 /**
  Creates an `NSMutableURLRequest` object with the specified HTTP method and URLString, and constructs a `multipart/form-data` HTTP body, using the specified parameters and multipart form data block. See http://www.w3.org/TR/html4/interact/forms.html#h-17.13.4.2