Make the method name more descriptive

Author: kkafar

ios/RNSScreenStackHeaderConfig.h

@@ -12,7 +12,7 @@
 
 @interface NSString (RNSStringUtil)
 
-+ (BOOL)rnscreens_isBlank:(nullable NSString *)string;
++ (BOOL)rnscreens_isBlankOrNull:(nullable NSString *)string;
 
 @end
 

ios/RNSScreenStackHeaderConfig.mm

@@ -49,7 +49,7 @@ @interface RCTImageLoader (Private)
 
 @implementation NSString (RNSStringUtil)
 
-+ (BOOL)rnscreens_isBlank:(NSString *)string
++ (BOOL)rnscreens_isBlankOrNull:(NSString *)string
 {
   if (string == nil) {
     return YES;
@@ -621,7 +621,7 @@ + (void)updateViewController:(UIViewController *)vc
   }
 
 #if !TARGET_OS_TV
-  const auto isBackTitleBlank = [NSString rnscreens_isBlank:config.backTitle] == YES;
+  const auto isBackTitleBlank = [NSString rnscreens_isBlankOrNull:config.backTitle] == YES;
   NSString *resolvedBackTitle = isBackTitleBlank ? prevItem.title : config.backTitle;
   RNSUIBarButtonItem *backBarButtonItem = [[RNSUIBarButtonItem alloc] initWithTitle:resolvedBackTitle
                                                                               style:UIBarButtonItemStylePlain