Nullable -> nonnull;

README.md

@@ -9,7 +9,7 @@ bring `UINavigationBar` to` UIViewController`.
 
 ## Introduction
 
-[KMNavigationBarTransition](https://github.com/MoZhouqi/KMNavigationBarTransition) provide a grace method deal with `navigationBar` transition, and requires zero  line of code changes, which is awesome.
+[KMNavigationBarTransition](https://github.com/MoZhouqi/KMNavigationBarTransition) provides a grace method deal with `navigationBar` transition, and requires zero  line of code changes, which is awesome.
 
 Here is the situation I couldn't doing well by using [KMNavigationBarTransition](https://github.com/MoZhouqi/KMNavigationBarTransition): first page is a product list, click product line, push to product details page, requires transparent `navigationBar`, while you scrolling, it could recover to default `navigationBar`'s appearance. Continue  push to the next page, the `navigationBar` needs to look like the first page, which is the default appearance. (like the following 1st gif tells.)
 

Sources/UIViewController+RRNavigationBar.h

@@ -13,6 +13,6 @@
 /// Define a different look like UINavigationBar for specific ViewController, assigin to this property.
 /// Try not change `translucent` property, which is may cause navigationBar flash when animation complete with extends container ViewController's view backgroundColor.
 /// `hidden`property will have no effect, try use `setBackgroundImage:forBarMetrics:` & `shadowImage` make navigationBar invisible.
-@property (nonatomic, strong, nullable) UINavigationBar *rr_navigationBar;
+@property (nonatomic, strong, nonnull) UINavigationBar *rr_navigationBar;
 
 @end

Sources/UIViewController+RRNavigationBar.m

@@ -41,7 +41,7 @@ - (void)set_rr_equalNavigationBarInTransition:(BOOL)_rr_equalNavigationBarInTran
 
 #pragma mark - Public
 
-- (UINavigationBar *)rr_navigationBar {
+- (nonnull UINavigationBar *)rr_navigationBar {
     UINavigationBar *bar = objc_getAssociatedObject(self, _cmd);
     if (bar) {
         return bar;
@@ -55,7 +55,7 @@ - (UINavigationBar *)rr_navigationBar {
     return bar;
 }
 
-- (void)setRr_navigationBar:(UINavigationBar *)rr_navigationBar {
+- (void)setRr_navigationBar:(nonnull UINavigationBar *)rr_navigationBar {
     objc_setAssociatedObject(self, @selector(rr_navigationBar), rr_navigationBar, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
     rr_navigationBar._holder = self;
 }