Change LM75AD output when no valid reading received from 0 to null (#24263)

CHANGELOG.md

@@ -13,6 +13,7 @@ All notable changes to this project will be documented in this file.
 - ESP8266 platform update from 2025.10.00 to 2025.12.00 (#24254)
 - ESP32 Platform from 2025.12.30 to 2025.12.31, Framework (Arduino Core) from v3.1.7 to v3.1.8 and IDF from v5.3.4.251205 to v5.3.4.251223 (#24254)
 - Refactor Adafruit Seesaw soil driver (#24270)
+- LM75AD output when no valid reading received from 0 to null (#24263)
 
 ### Fixed
 - ESP32 BLE not starting (#24240)

RELEASENOTES.md

@@ -123,6 +123,7 @@ The latter links can be used for OTA upgrades too like ``OtaUrl https://ota.tasm
 - Vid6608 library from v1.0.2 to v1.0.3 [#24218](https://github.com/arendst/Tasmota/issues/24218)
 - IRremoteESP8266 library from v2.8.6 to v2.8.6-ca474a6 [#24226](https://github.com/arendst/Tasmota/issues/24226)
 - Refactor Adafruit Seesaw soil driver [#24270](https://github.com/arendst/Tasmota/issues/24270)
+- LM75AD output when no valid reading received from 0 to null [#24263](https://github.com/arendst/Tasmota/issues/24263)
 - Update Zigbee WebUI [#24224](https://github.com/arendst/Tasmota/issues/24224)
 
 ### Fixed

tasmota/tasmota_xsns_sensor/xsns_26_lm75ad.ino

@@ -68,16 +68,18 @@ void LM75ADDetect(void) {
 }
 
 float LM75ADGetTemp(void) {
+  uint16_t t;
+  if (I2cValidRead16(&t, lm75ad_address, LM75_TEMP_REGISTER, lm75ad_bus)) {
     int16_t sign = 1;
-
-  uint16_t t = I2cRead16(lm75ad_address, LM75_TEMP_REGISTER, lm75ad_bus);
-  if (t & 0x8000) { // we are getting a negative temperature value
+    if (t & 0x8000) { // We are getting a negative temperature value
       t = (~t) +0x20;
       sign = -1;
     }
-  t = t >> 5; // shift value into place (5 LSB not used)
+    t = t >> 5; // Shift value into place (5 LSB not used)
     return ConvertTemp(sign * t * 0.125f);
   }
+  return NAN;  // Will be changed to "null" by ext_vsprintf_P()
+}
 
 void LM75ADShow(bool json) {
   float t = LM75ADGetTemp();