Replace all NULL with nullptr

Bug: angleproject:1695

Change-Id: Ide0591ffdad5815385a4d805b320a32533bcc03a
Reviewed-on: https://chromium-review.googlesource.com/883681
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Luc Ferron <lucferron@google.com>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index ba7e73f..7a12983 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -2922,7 +2922,7 @@
     {
         gl::Texture *tex = context->getTexture(texture);
 
-        if (tex == NULL)
+        if (tex == nullptr)
         {
             context->handleError(InvalidOperation());
             return false;