Fix exception when electrical power is not available for a clamp

[firepinn]

2023-12-16 12:34:43.308 ERROR (MainThread) [homeassistant.components.sensor] Error adding entities for domain sensor with platform nhc2 Traceback (most recent call last): File "/usr/src/homeassistant/homeassistant/helpers/entity_platform.py", line 509, in async_add_entities await asyncio.gather(*tasks) File "/usr/src/homeassistant/homeassistant/helpers/entity_platform.py", line 754, in _async_add_entity await entity.add_to_platform_finish() File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 1025, in add_to_platform_finish self.async_write_ha_state() File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 745, in async_write_ha_state self._async_write_ha_state() File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 845, in _async_write_ha_state state, attr = self._async_generate_attributes() ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 786, in _async_generate_attributes state = self._stringify_state(available) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 751, in _stringify_state if (state := self.state) is None: ^^^^^^^^^^ File "/usr/src/homeassistant/homeassistant/components/sensor/init.py", line 501, in state value = self.native_value ^^^^^^^^^^^^^^^^^ File "/config/custom_components/nhc2/entities/electricity_clamp_centralmeter_electrical_power_consumption.py", line 50, in native_value if self._device.electrical_power > 0: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TypeError: '>' not supported between instances of 'NoneType' and 'int'