Add sanity check for label value

Signed-off-by: Pengfei Zhang <andysim3d@gmail.com>

.gitignore

@@ -7,4 +7,5 @@ dist
 .coverage
 .tox
 .*cache
-htmlcov
+htmlcov
+.vs/

prometheus_client/metrics.py

@@ -706,6 +706,8 @@ def info(self, val: Dict[str, str]) -> None:
             raise ValueError('Overlapping labels for Info metric, metric: {} child: {}'.format(
                 self._labelnames, val))
         with self._lock:
+            if any(i is None for i in val.values()):
+                raise ValueError('Label value cannot be None')
             self._value = dict(val)
 
     def _child_samples(self) -> Iterable[Sample]:

tests/test_core.py

@@ -534,6 +534,7 @@ def test_info(self):
 
     def test_labels(self):
         self.assertRaises(ValueError, self.labels.labels('a').info, {'l': ''})
+        self.assertRaises(ValueError, self.labels.labels('a').info, {'il': None})
 
         self.labels.labels('a').info({'foo': 'bar'})
         self.assertEqual(1, self.registry.get_sample_value('il_info', {'l': 'a', 'foo': 'bar'}))