[binder] Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: Icae41e24bc3dc2cc81ddb14978d1f6c1e52061f5
diff --git a/libs/binder/tests/binderLibTest.cpp b/libs/binder/tests/binderLibTest.cpp
index f23ac52..73c2eba 100644
--- a/libs/binder/tests/binderLibTest.cpp
+++ b/libs/binder/tests/binderLibTest.cpp
@@ -1189,7 +1189,7 @@
                     return ret;
                 }
                 buf = data.readInplace(size);
-                if (buf == NULL) {
+                if (buf == nullptr) {
                     return BAD_VALUE;
                 }
                 ret = write(fd.get(), buf, size);