Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: Id869744db54b5b366454a5e13b467ac1f4df2845
diff --git a/cmdline/cmdline_parser_test.cc b/cmdline/cmdline_parser_test.cc
index a52e163..a33d537 100644
--- a/cmdline/cmdline_parser_test.cc
+++ b/cmdline/cmdline_parser_test.cc
@@ -59,7 +59,7 @@
   template <typename T>
   bool UsuallyEquals(const T& expected, const T& actual,
                      typename std::enable_if<
-                         detail::SupportsEqualityOperator<T>::value>::type* = 0) {
+                         detail::SupportsEqualityOperator<T>::value>::type* = nullptr) {
     return expected == actual;
   }
 
@@ -73,8 +73,8 @@
   template <typename T, typename ... Ignore>
   bool UsuallyEquals(const T& expected, const T& actual,
                      const Ignore& ... more ATTRIBUTE_UNUSED,
-                     typename std::enable_if<std::is_pod<T>::value>::type* = 0,
-                     typename std::enable_if<!detail::SupportsEqualityOperator<T>::value>::type* = 0
+                     typename std::enable_if<std::is_pod<T>::value>::type* = nullptr,
+                     typename std::enable_if<!detail::SupportsEqualityOperator<T>::value>::type* = nullptr
                      ) {
     return memcmp(std::addressof(expected), std::addressof(actual), sizeof(T)) == 0;
   }