使用 nil coalescing 减少行数

如题

MJRefresh/Custom/Header/MJRefreshNormalHeader.m

@@ -20,10 +20,7 @@ @implementation MJRefreshNormalHeader
 - (UIImageView *)arrowView
 {
     if (!_arrowView) {
-        UIImage *image = [UIImage imageNamed:MJRefreshSrcName(@"arrow.png")];
-        if (!image) {
-            image = [UIImage imageNamed:MJRefreshFrameworkSrcName(@"arrow.png")];
-        }
+        UIImage *image = [UIImage imageNamed:MJRefreshSrcName(@"arrow.png")] ?: [UIImage imageNamed:MJRefreshFrameworkSrcName(@"arrow.png")];
         UIImageView *arrowView = [[UIImageView alloc] initWithImage:image];
         [self addSubview:_arrowView = arrowView];
     }