Remove CUIICatalog invalid asset name supplied error

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Closes facebook#7535

Differential Revision: D3509757

fbshipit-source-id: 70ff6c9c137c766ccb1173921f08571f48cb4f0b

React/Base/RCTConvert.m

@@ -900,7 +900,7 @@ + (UIImage *)UIImage:(id)json
   NSString *scheme = URL.scheme.lowercaseString;
   if ([scheme isEqualToString:@"file"]) {
     NSString *assetName = RCTBundlePathForURL(URL);
-    image = [UIImage imageNamed:assetName];
+    image = assetName ? [UIImage imageNamed:assetName] : nil;
     if (!image) {
       // Attempt to load from the file system
       NSString *filePath = URL.path;