[libs/ui] Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: I240d39ef4328943447149700b3ece371681078d1
diff --git a/libs/ui/Region.cpp b/libs/ui/Region.cpp
index 3bd3748..224dc2c 100644
--- a/libs/ui/Region.cpp
+++ b/libs/ui/Region.cpp
@@ -820,7 +820,7 @@
     }
 
     if (numRects > (UINT32_MAX / sizeof(Rect))) {
-        android_errorWriteWithInfoLog(0x534e4554, "29983260", -1, NULL, 0);
+        android_errorWriteWithInfoLog(0x534e4554, "29983260", -1, nullptr, 0);
         return NO_MEMORY;
     }