add some nullability annotations for swift

Author: isaced

FEPopupMenuController/FEPopupMenuController.h

@@ -53,7 +53,7 @@
 /**
  *  the content view background color, default is white
  */
-@property (nonatomic, strong) UIColor *contentViewBackgroundColor;
+@property (nonatomic, strong) UIColor * __nonnull contentViewBackgroundColor;
 
 /**
  *  the content view corner radius, default is 8.0

FEPopupMenuController/FEPopupMenuItem.h

@@ -16,26 +16,26 @@ typedef void(^FEPopupMenuItemActionBlock)(void);
 /**
  *  init FEPopupMenuItem with title text and icon image
  */
-- (instancetype __nonnull)initWithTitle:(NSString *)title iconImage:(UIImage *)iconImage action:(FEPopupMenuItemActionBlock)action;
+- (instancetype __nonnull)initWithTitle:(NSString * __nonnull)title iconImage:(UIImage * __nonnull)iconImage action:(FEPopupMenuItemActionBlock __nullable)action;
 
 /**
  *  title of item
  */
-@property (nonatomic, copy) NSString *title;
+@property (nonatomic, copy) NSString * __nullable title;
 
 /**
  *  icon image of item
  */
-@property (nonatomic, strong) UIImage *iconImage;
+@property (nonatomic, strong) UIImage * __nullable iconImage;
 
 /**
  *  callback of item when selected
  */
-@property (nonatomic, copy) FEPopupMenuItemActionBlock action;
+@property (nonatomic, copy) FEPopupMenuItemActionBlock __nullable action;
 
 /**
  *  the color of title
  */
-@property (nonatomic, strong) UIColor *titleColor;
+@property (nonatomic, strong) UIColor * __nullable titleColor;
 
 @end