shill: Replace NULL with nullptr.

BUG=None
TEST=`USE=wimax FEATURES=test emerge-$BOARD shill`

Change-Id: I30ab47ff32dcadad09ae7a2baf4d4123a6ef0d8e
Reviewed-on: https://chromium-review.googlesource.com/220657
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
diff --git a/mock_eap_listener.cc b/mock_eap_listener.cc
index e738c29..adf30cb 100644
--- a/mock_eap_listener.cc
+++ b/mock_eap_listener.cc
@@ -6,7 +6,7 @@
 
 namespace shill {
 
-MockEapListener::MockEapListener() : EapListener(NULL, 0) {}
+MockEapListener::MockEapListener() : EapListener(nullptr, 0) {}
 
 MockEapListener::~MockEapListener() {}