swift api compatibility

YYModel/NSObject+YYModel.h

@@ -300,7 +300,7 @@ NS_ASSUME_NONNULL_BEGIN
  
  @return A custom mapper for properties.
  */
-+ (NSDictionary<NSString *, id> *)modelCustomPropertyMapper;
++ (nullable NSDictionary<NSString *, id> *)modelCustomPropertyMapper;
 
 /**
  The generic class mapper for container properties.
@@ -329,7 +329,7 @@ NS_ASSUME_NONNULL_BEGIN
  
  @return A class mapper.
  */
-+ (NSDictionary<NSString *, id> *)modelContainerPropertyGenericClass;
++ (nullable NSDictionary<NSString *, id> *)modelContainerPropertyGenericClass;
 
 /**
  If you need to create instances of different classes during json->object transform,
@@ -371,7 +371,7 @@ NS_ASSUME_NONNULL_BEGIN
  
  @return An array of property's name.
  */
-+ (NSArray<NSString *> *)modelPropertyBlacklist;
++ (nullable NSArray<NSString *> *)modelPropertyBlacklist;
 
 /**
  If a property is not in the whitelist, it will be ignored in model transform process.
@@ -379,7 +379,7 @@ NS_ASSUME_NONNULL_BEGIN
  
  @return An array of property's name.
  */
-+ (NSArray<NSString *> *)modelPropertyWhitelist;
++ (nullable NSArray<NSString *> *)modelPropertyWhitelist;
 
 /**
  If the default json-to-model transform does not fit to your model object, implement

YYModel/YYClassInfo.h

@@ -106,7 +106,7 @@ YYEncodingType YYEncodingGetType(const char *typeEncoding);
 @property (nonatomic, assign, readonly) IMP imp;                        ///< method's implementation
 @property (nonatomic, strong, readonly) NSString *typeEncoding;         ///< method's parameter and return types
 @property (nonatomic, strong, readonly) NSString *returnTypeEncoding;   ///< return value's type
-@property (nonatomic, strong, readonly) NSArray<NSString *> *argumentTypeEncodings; ///< array of arguments' type
+@property (nullable, nonatomic, strong, readonly) NSArray<NSString *> *argumentTypeEncodings; ///< array of arguments' type
 
 /**
  Creates and returns a method info object.
@@ -148,7 +148,7 @@ YYEncodingType YYEncodingGetType(const char *typeEncoding);
 @property (nonatomic, assign, readonly) Class cls; ///< class object
 @property (nullable, nonatomic, assign, readonly) Class superCls; ///< super class object
 @property (nullable, nonatomic, assign, readonly) Class metaCls;  ///< class's meta class object
-@property (nonatomic, assign, readonly) BOOL isMeta; ///< whether this class is meta class
+@property (nonatomic, readonly) BOOL isMeta; ///< whether this class is meta class
 @property (nonatomic, strong, readonly) NSString *name; ///< class name
 @property (nullable, nonatomic, strong, readonly) YYClassInfo *superClassInfo; ///< super class's class info
 @property (nullable, nonatomic, strong, readonly) NSDictionary<NSString *, YYClassIvarInfo *> *ivarInfos; ///< ivars