L3 oemcrypto: Replace NULL with nullptr

Merge from Widevine repo of https://widevine-internal-review.git.corp.google.com/c/cdm/+/95206

Only one file is affected in Android repo.

Bug: 149050172
Test: Unit tests
Change-Id: I3251b9997733e59b18c0b5727205067dcc3a963c

libwvdrmengine/oemcrypto/renewal/derive_key.cpp

@@ -85,7 +85,7 @@ static std::string GetSSLError() {
 static bool DeriveKey(const std::vector<uint8_t>& key,
                       const std::vector<uint8_t>& context,
                       std::vector<uint8_t>* out) {
-  if (key.empty() || context.empty() || out == NULL) {
+  if (key.empty() || context.empty() || out == nullptr) {
     std::cerr << "DeriveKey(): Invalid inputs" << std::endl;
     return false;
   }