Merge pull request #2734 from shcheklein/fix-get-npe

fix NPE when we do get that does not provide progress callback

dvc/output/base.py

@@ -287,7 +287,8 @@ class OutputBase(object):
 
     def checkout(self, force=False, progress_callback=None, tag=None):
         if not self.use_cache:
-            progress_callback(str(self.path_info), self.get_files_number())
+            if progress_callback:
+                progress_callback(str(self.path_info), self.get_files_number())
             return None
 
         if tag: