libchromeos: Replace NULL with nullptr

BUG=None
TEST=FEATURES=test emerge-link libchromeos

Change-Id: I41c74e364a8299e148db3e81e5146755cc3e45ea
Reviewed-on: https://chromium-review.googlesource.com/214833
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/chromeos/policy/device_policy_impl.cc b/chromeos/policy/device_policy_impl.cc
index d468a73..1aab39a 100644
--- a/chromeos/policy/device_policy_impl.cc
+++ b/chromeos/policy/device_policy_impl.cc
@@ -52,7 +52,7 @@
     return false;
   }
 
-  EVP_PKEY* public_key_ssl = d2i_PUBKEY_bio(bio, NULL);
+  EVP_PKEY* public_key_ssl = d2i_PUBKEY_bio(bio, nullptr);
   if (!public_key_ssl) {
     BIO_free_all(bio);
     EVP_MD_CTX_cleanup(&ctx);
@@ -61,7 +61,7 @@
 
   const unsigned char* sig =
       reinterpret_cast<const unsigned char*>(signature.data());
-  int rv = EVP_VerifyInit_ex(&ctx, digest, NULL);
+  int rv = EVP_VerifyInit_ex(&ctx, digest, nullptr);
   if (rv == 1) {
     EVP_VerifyUpdate(&ctx, signed_data.data(), signed_data.length());
     rv = EVP_VerifyFinal(&ctx,