renew_metadata fails, if metadata file is empty/corrupted

[bugy]

20-Sep-2017 13:30:13 | Traceback (most recent call last):
-- | --
20-Sep-2017 13:30:13 | File "ci_rebuild.py", line 904, in <module>
20-Sep-2017 13:30:13 | incremental_rebuild(last_revision, current_revision)
20-Sep-2017 13:30:13 | File "ci_rebuild.py", line 897, in incremental_rebuild
20-Sep-2017 13:30:13 | fast_install(unchanged_project, MAVEN_REPO_PATH)
20-Sep-2017 13:30:13 | File "ci_rebuild.py", line 863, in fast_install
20-Sep-2017 13:30:13 | renew_metadata([project], repo_path)
20-Sep-2017 13:30:13 | File "ci_rebuild.py", line 767, in renew_metadata
20-Sep-2017 13:30:13 | "versioning/snapshotVersions/snapshotVersion/updated": current_time
20-Sep-2017 13:30:13 | File "ci_rebuild.py", line 310, in replace_in_tree
20-Sep-2017 13:30:13 | tree = ElementTree.parse(file_path)
20-Sep-2017 13:30:13 | File "/tex/python/python/lib/python2.7/xml/etree/ElementTree.py", line 1182, in parse
20-Sep-2017 13:30:13 | tree.parse(source, parser)
20-Sep-2017 13:30:13 | File "/tex/python/python/lib/python2.7/xml/etree/ElementTree.py", line 657, in parse
20-Sep-2017 13:30:13 | self._root = parser.close()
20-Sep-2017 13:30:13 | File "/tex/python/python/lib/python2.7/xml/etree/ElementTree.py", line 1665, in close
20-Sep-2017 13:30:13 | self._raiseerror(v)
20-Sep-2017 13:30:13 | File "/tex/python/python/lib/python2.7/xml/etree/ElementTree.py", line 1517, in _raiseerror
20-Sep-2017 13:30:13 | raise err
20-Sep-2017 13:30:13 | xml.etree.ElementTree.ParseError: no element found: line 1, column 0