When reporting, don't fall over if there's no data to report on. Fixes issue #37.

1 files changed, 4 insertions, 1 deletions

diff --git a/coverage/report.py b/coverage/report.py
index 7f3e3e02..c2215521 100644
--- a/coverage/report.py
+++ b/coverage/report.py
@@ -2,7 +2,7 @@
 
 import os
 from coverage.codeunit import code_unit_factory
-from coverage.misc import NoSource
+from coverage.misc import CoverageException, NoSource
 
 class Reporter(object):
     """A base class for all reporters."""
@@ -45,6 +45,9 @@ class Reporter(object):
         """
         self.find_code_units(morfs, omit_prefixes)
 
+        if not self.code_units:
+            raise CoverageException("No data to report.")
+
         self.directory = directory
         if self.directory and not os.path.exists(self.directory):
             os.makedirs(self.directory)