autopkgtest: Don't cache results for undefined versions

If a result.tar does not contain a testpkg-version, we must still match it
against pending.txt, but we must not add it to the results cache. This ends up
being a "null" version key (JSON's serialization of None) which becomes an
actual version string once this is read back.

autopkgtest.py

@@ -398,11 +398,12 @@ class AutoPackageTest(object):
 
         # add this result
         src_arch_results = self.test_results.setdefault(src, {}).setdefault(arch, [stamp, {}, False])
-        if passed:
-            # update ever_passed field
-            src_arch_results[2] = True
-        src_arch_results[1][ver] = (passed, merge_triggers(
-            src_arch_results[1].get(ver, (None, []))[1], satisfied_triggers))
+        if ver is not None:
+            if passed:
+                # update ever_passed field
+                src_arch_results[2] = True
+            src_arch_results[1][ver] = (passed, merge_triggers(
+                src_arch_results[1].get(ver, (None, []))[1], satisfied_triggers))
         # update latest_stamp
         if stamp > src_arch_results[0]:
             src_arch_results[0] = stamp

tests/test_autopkgtest.py

@@ -818,6 +818,21 @@ lightgreen 1 i386 green 3
 
         self.assertEqual(self.pending_requests, '')
 
+        # one more tmpfail result, should not confuse britney with None version
+        self.swift.set_results({'autopkgtest-series': {
+            'series/i386/l/lightgreen/20150101_100201@': (16, None),
+        }})
+        self.do_test(
+            [],
+            NOT_CONSIDERED,
+            [r'\blightgreen\b.*>1</a> to .*>2<',
+             r'autopkgtest for lightgreen 2: .*amd64.*Regression.*i386.*Regression'],
+            ['in progress'])
+        with open(os.path.join(self.data.path, 'data/series-proposed/autopkgtest/results.cache')) as f:
+            contents = f.read()
+        self.assertNotIn('null', contents)
+        self.assertNotIn('None', contents)
+
     def test_rerun_failure(self):
         '''manually re-running failed tests gets picked up'''