Failsafe a very common usage error (passing URL as NSString instead of NSURL)

@@ -73,6 +73,13 @@ static SDWebImageManager *instance;
         return;
     }
 
+    // Very common mistake is to send the URL using NSString object instead of NSURL. For some strange reason, XCode won't
+    // throw any warning for this type mismatch. Here we failsafe this error by allowing URLs to be passed as NSString.
+    if ([url isKindOfClass:NSString.class])
+    {
+        url = [NSURL URLWithString:(NSString *)url];
+    }
+
     // Check the on-disk cache async so we don't block the main thread
     [cacheDelegates addObject:delegate];
     NSDictionary *info = [NSDictionary dictionaryWithObjectsAndKeys:delegate, @"delegate", url, @"url", [NSNumber numberWithBool:lowPriority], @"low_priority", nil];