Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: I4e29baf95b16942b22bbd15c50aa956f5decf241
diff --git a/AccessControl.cpp b/AccessControl.cpp
index 93d78e2..0c73dc6 100644
--- a/AccessControl.cpp
+++ b/AccessControl.cpp
@@ -22,7 +22,7 @@
 
 AccessControl::AccessControl() {
     mSeHandle = selinux_android_hw_service_context_handle();
-    LOG_ALWAYS_FATAL_IF(mSeHandle == NULL, "Failed to acquire SELinux handle.");
+    LOG_ALWAYS_FATAL_IF(mSeHandle == nullptr, "Failed to acquire SELinux handle.");
 
     if (getcon(&mSeContext) != 0) {
         LOG_ALWAYS_FATAL("Failed to acquire hwservicemanager context.");
@@ -64,7 +64,7 @@
 }
 
 Context AccessControl::getContext(pid_t sourcePid) {
-    char *sourceContext = NULL;
+    char *sourceContext = nullptr;
 
     if (getpidcon(sourcePid, &sourceContext) < 0) {
         ALOGE("SELinux: failed to retrieve process context for pid %d", sourcePid);
@@ -92,7 +92,7 @@
 }
 
 bool AccessControl::checkPermission(const Context &context, pid_t sourceAuditPid, const char *perm, const char *interface) {
-    char *targetContext = NULL;
+    char *targetContext = nullptr;
     bool allowed = false;
 
     // Lookup service in hwservice_contexts