1 files changed, 3 insertions, 0 deletions
diff --git a/coverage/data.py b/coverage/data.py
index e393345a..71d6624d 100644
--- a/coverage/data.py
+++ b/coverage/data.py
@@ -253,6 +253,9 @@ class CoverageJsonData(object):
             return self._file_tracers.get(filename, "")
         return None
 
+    def contexts_by_lineno(self, filename):
+        return collections.defaultdict(list)
+
     def run_infos(self):
         """Return the list of dicts of run information.