commit c626c54074b36edb090254fe6f4985bc20893436
Author: Michal Domonkos <mdomonko@redhat.com>
Date:   Thu Mar 23 16:05:16 2017 +0100

    modifyrepo: handle empty file with LZMA. BZ 1287685
    
    When trying to compress an empty string with LZMA, we will get the
    unfriendly "LZMA.error: unknown error!".  Let's handle this case
    ourselves and raise a more user-friendly error instead.

diff --git a/modifyrepo.py b/modifyrepo.py
index 34b0902..ade5607 100755
--- a/modifyrepo.py
+++ b/modifyrepo.py
@@ -125,6 +125,9 @@ class RepoMetadata:
         else:
             raise MDError, 'invalid metadata type'
 
+        if not md and self.compress_type == 'xz':
+            raise MDError, 'LZMA does not support compressing empty files'
+
         ## Compress the metadata and move it into the repodata
         mdtype = self._get_mdtype(mdname, mdtype)
         destmd = os.path.join(self.repodir, mdname)