clang-tidy: Replace NULL with nullptr

Replaced all instances of NULL with nullptr to improve type safety
and clarity, as nullptr is the modern C++ standard for null pointers.

Tested: Build verified

Change-Id: Ia40d9435ab57651ec6d13d5408cf69130043fa79
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/sensorhandler.cpp b/sensorhandler.cpp
index e40fa49..134eaa6 100644
--- a/sensorhandler.cpp
+++ b/sensorhandler.cpp
@@ -269,7 +269,7 @@
     dbus_interface_t a;
     int r;
     sd_bus_error error = SD_BUS_ERROR_NULL;
-    sd_bus_message* m = NULL;
+    sd_bus_message* m = nullptr;
 
     r = find_openbmc_path(number, &a);
 
@@ -296,7 +296,7 @@
         goto final;
     }
 
-    r = sd_bus_call(bus, m, 0, &error, NULL);
+    r = sd_bus_call(bus, m, 0, &error, nullptr);
     if (r < 0)
     {
         std::fprintf(stderr, "Failed to call the method: %s", strerror(-r));
@@ -314,7 +314,7 @@
     dbus_interface_t a;
     int r;
     sd_bus_error error = SD_BUS_ERROR_NULL;
-    sd_bus_message* m = NULL;
+    sd_bus_message* m = nullptr;
 
     r = find_openbmc_path(number, &a);
 
@@ -341,7 +341,7 @@
         goto final;
     }
 
-    r = sd_bus_call(bus, m, 0, &error, NULL);
+    r = sd_bus_call(bus, m, 0, &error, nullptr);
     if (r < 0)
     {
         std::fprintf(stderr, "12 Failed to call the method: %s", strerror(-r));