Allow clearing optional weather sources in Options

Optional weather source fields used the current selection as the form
default. A cleared field that the frontend omits was refilled with the
old sources by voluptuous, and an options key missing from the
submission fell back to the original setup data. Optional providers
could therefore not be removed in the UI.

Pre-fill with suggested values instead, and save omitted optional lists
as empty so they override older entry data. No UI strings changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ha/test_config_flow.py

@@ -4,6 +4,7 @@ from homeassistant.data_entry_flow import FlowResultType
 from pytest_homeassistant_custom_component.common import MockConfigEntry
 
 from custom_components.heating_mpc.const import DOMAIN
+from custom_components.heating_mpc.weather_sources import sources_for
 
 
 async def test_config_flow(hass, inputs):
@@ -56,3 +57,35 @@ async def test_v1_entry_migrates_on_setup(hass, inputs):
     assert entry.version == 2
     assert entry.data["outside_temperature_sources"] == ["sensor.outside"]
     assert "outside_entity" not in entry.data
+
+
+async def test_options_flow_clears_optional_weather_sources(hass, inputs):
+    """Swapping providers in the UI must allow removing an optional source list."""
+    entry = MockConfigEntry(domain=DOMAIN, version=2, unique_id="home_heating", data={
+        "climate_entity": "climate.reference", "heater_entity": "switch.boiler",
+        "room_entities": ["sensor.room"], "outside_temperature_sources": ["sensor.outside"],
+        "outside_wind_sources": ["sensor.wind"], "outside_pressure_sources": ["sensor.pressure"],
+        "weights": {"sensor.room": 1.0}})
+    entry.add_to_hass(hass)
+    assert await hass.config_entries.async_setup(entry.entry_id)
+    await hass.async_block_till_done()
+    flow = hass.config_entries.options
+    result = await flow.async_init(entry.entry_id)
+    result = await flow.async_configure(result["flow_id"], result["data_schema"]({
+        "climate_entity": "climate.reference", "heater_entity": "switch.boiler",
+        "room_entities": ["sensor.room"]}))
+    markers = {str(key): key for key in result["data_schema"].schema}
+    assert markers["outside_wind_sources"].description == {"suggested_value": ["sensor.wind"]}
+    # The user removes the wind provider; a cleared field may be omitted on submit.
+    result = await flow.async_configure(result["flow_id"], result["data_schema"](
+        {"outside_temperature_sources": ["sensor.outside"]}))
+    result = await flow.async_configure(result["flow_id"], result["data_schema"](
+        {"outside_pressure_sources": ["sensor.pressure"]}))
+    result = await flow.async_configure(result["flow_id"], {"weight__sensor.room": 1})
+    assert result["type"] is FlowResultType.CREATE_ENTRY
+    await hass.async_block_till_done()
+    assert entry.options["outside_wind_sources"] == []
+    assert entry.options["outside_pressure_sources"] == ["sensor.pressure"]
+    config = hass.data[DOMAIN][entry.entry_id].config
+    assert sources_for(config, "wind") == []
+    assert sources_for(config, "pressure") == ["sensor.pressure"]