Gracefully handle case where dependency_mapping_files is empty
RELNOTES: None
@@ -405,6 +405,8 @@ def BuildArtifactSourceTree(files, file_open=open):
corresponding direct dependent source files.
"""
tree = dict()
+ if not files:
+ return tree
for filename in files.split(','):
with file_open(filename, 'r') as f:
for line in f:
