The Appearance property might not be available, and would cause
warnings like:
upowerd[17733]: g_variant_get_type: assertion 'value != NULL' failed
upowerd[17733]: g_variant_type_is_subtype_of: assertion 'g_variant_type_check (type)' failed
upowerd[17733]: g_variant_get_uint16: assertion 'g_variant_is_of_type (value, G_VARIANT_TYPE_UINT16)' failed