mercurial/context.py

--- a/mercurial/context.py	Fri May 10 10:23:08 2019 -0700
+++ b/mercurial/context.py	Fri May 10 11:03:54 2019 -0700
@@ -1913,7 +1913,7 @@
         if self.isdirty(path):
             return self._cache[path]['copied']
         else:
-            raise error.ProgrammingError('copydata() called on clean context')
+            return None
 
     def flags(self, path):
         if self.isdirty(path):