Fix empty default ZHA configuration (#79475)

* Also add 0 as a default for transition in const.py

This is the same default transition (none) that is used in ZHA's light.py

* Send default values for unconfigured options in ZHA's configuration API

* Remove options that match defaults values before saving

homeassistant/components/zha/api.py

@@ -1028,6 +1028,12 @@ async def websocket_get_configuration(
         data["data"][section] = zha_gateway.config_entry.options.get(
             CUSTOM_CONFIGURATION, {}
         ).get(section, {})
+
+        # send default values for unconfigured options
+        for entry in data["schemas"][section]:
+            if data["data"][section].get(entry["name"]) is None:
+                data["data"][section][entry["name"]] = entry["default"]
+
     connection.send_result(msg[ID], data)
 
 
@@ -1047,6 +1053,22 @@ async def websocket_update_zha_configuration(
     options = zha_gateway.config_entry.options
     data_to_save = {**options, **{CUSTOM_CONFIGURATION: msg["data"]}}
 
+    for section, schema in ZHA_CONFIG_SCHEMAS.items():
+        for entry in schema.schema:
+            # remove options that match defaults
+            if (
+                data_to_save[CUSTOM_CONFIGURATION].get(section, {}).get(entry)
+                == entry.default()
+            ):
+                data_to_save[CUSTOM_CONFIGURATION][section].pop(entry)
+            # remove entire section block if empty
+            if not data_to_save[CUSTOM_CONFIGURATION][section]:
+                data_to_save[CUSTOM_CONFIGURATION].pop(section)
+
+    # remove entire custom_configuration block if empty
+    if not data_to_save[CUSTOM_CONFIGURATION]:
+        data_to_save.pop(CUSTOM_CONFIGURATION)
+
     _LOGGER.info(
         "Updating ZHA custom configuration options from %s to %s",
         options,

homeassistant/components/zha/core/const.py

@@ -146,7 +146,7 @@ CONF_DEFAULT_CONSIDER_UNAVAILABLE_BATTERY = 60 * 60 * 6  # 6 hours
 
 CONF_ZHA_OPTIONS_SCHEMA = vol.Schema(
     {
-        vol.Optional(CONF_DEFAULT_LIGHT_TRANSITION): cv.positive_int,
+        vol.Optional(CONF_DEFAULT_LIGHT_TRANSITION, default=0): cv.positive_int,
         vol.Required(CONF_ENABLE_ENHANCED_LIGHT_TRANSITION, default=False): cv.boolean,
         vol.Required(CONF_ENABLE_LIGHT_TRANSITIONING_FLAG, default=True): cv.boolean,
         vol.Required(CONF_ALWAYS_PREFER_XY_COLOR_MODE, default=True): cv.boolean,