Fix statistics for binary sensor (#18764)

* Fix statistics for binary sensor

-) Binary sensors have 'on' and 'off' for state resulting in issue as numbers were expected. Fixed so that it works with non-numeric states as well.
-) Added check to skip unknown states.
-) Updates test so that binary sensor test will use non-numeric values for states.

* Using guard clause and changed debug to error

Changed to use a guard clause for state unknown.
Writing error on value error instead of debug.

* Add docstring

homeassistant/components/sensor/statistics.py

@@ -120,7 +120,7 @@ class StatisticsSensor(Entity):
                 self.hass, self._entity_id, async_stats_sensor_state_listener)
 
             if 'recorder' in self.hass.config.components:
-                # only use the database if it's configured
+                # Only use the database if it's configured
                 self.hass.async_create_task(
                     self._async_initialize_from_database()
                 )
@@ -129,11 +129,20 @@ class StatisticsSensor(Entity):
             EVENT_HOMEASSISTANT_START, async_stats_sensor_startup)
 
     def _add_state_to_queue(self, new_state):
+        """Add the state to the queue."""
+        if new_state.state == STATE_UNKNOWN:
+            return
+
         try:
-            self.states.append(float(new_state.state))
+            if self.is_binary:
+                self.states.append(new_state.state)
+            else:
+                self.states.append(float(new_state.state))
+
             self.ages.append(new_state.last_updated)
         except ValueError:
-            pass
+            _LOGGER.error("%s: parsing error, expected number and received %s",
+                          self.entity_id, new_state.state)
 
     @property
     def name(self):

tests/components/sensor/test_statistics.py

@@ -40,7 +40,7 @@ class TestStatisticsSensor(unittest.TestCase):
 
     def test_binary_sensor_source(self):
         """Test if source is a sensor."""
-        values = [1, 0, 1, 0, 1, 0, 1]
+        values = ['on', 'off', 'on', 'off', 'on', 'off', 'on']
         assert setup_component(self.hass, 'sensor', {
             'sensor': {
                 'platform': 'statistics',