fix (siren): avoid clobbering the tone by trying to set it to null

When the tone does not need setting, the value is null, but the code was
blindly setting the tone even in this case. Check for null first, and skip
setting tone in that case.

PR #4048

custom_components/tuya_local/siren.py

@@ -87,10 +87,11 @@ class TuyaLocalSiren(TuyaLocalEntity, SirenEntity):
                 if tone == "off":
                     tone = self._default_tone
 
-            set_dps = {
-                **set_dps,
-                **self._tone_dp.get_values_to_set(self._device, tone, set_dps),
-            }
+            if tone is not None:
+                set_dps = {
+                    **set_dps,
+                    **self._tone_dp.get_values_to_set(self._device, tone, set_dps),
+                }
 
         if duration is not None and self._duration_dp:
             set_dps = {