raconverter 处理nsnull

common/RAConvertor.m

@@ -111,7 +111,7 @@ begin:
 +(NSDictionary*) string2dict:(NSString*) str
 {
     
-    if(str==nil)
+    if(str==nil||(NSNull *)str==[NSNull null])
         return nil;
     NSError *error = nil;
     NSDictionary *string2dic = [NSJSONSerialization JSONObjectWithData: [str dataUsingEncoding:NSUTF8StringEncoding]