change FileField.to_representation to EAFP style

rest_framework/fields.py

@@ -1546,16 +1546,15 @@ class FileField(Field):
             return None
 
         use_url = getattr(self, 'use_url', api_settings.UPLOADED_FILES_USE_URL)
-
         if use_url:
-            if not getattr(value, 'url', None):
-                # If the file has not been saved it may not have a URL.
+            try:
+                url = value.url
+                request = self.context.get('request', None)
+                if request is not None:
+                    return request.build_absolute_uri(url)
+                return url
+            except AttributeError:
                 return None
-            url = value.url
-            request = self.context.get('request', None)
-            if request is not None:
-                return request.build_absolute_uri(url)
-            return url
         return value.name