[cmds] Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: I1635395d653ace5a11c75795f4a7d2bf2d9e0b1b
Merged-In: I73a0a82e3e32001f8ffb0880250c7023dd8290d3
diff --git a/cmds/lshal/PipeRelay.cpp b/cmds/lshal/PipeRelay.cpp
index 3828bbf..87d75ac 100644
--- a/cmds/lshal/PipeRelay.cpp
+++ b/cmds/lshal/PipeRelay.cpp
@@ -78,7 +78,7 @@
 PipeRelay::~PipeRelay() {
     CloseFd(&mFds[1]);
 
-    if (mThread != NULL) {
+    if (mThread != nullptr) {
         mThread->join();
         mThread.clear();
     }