[clang-tidy] Add back a test with a custom NULL macro. Remove redundant default.

llvm-svn: 245533
diff --git a/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
index 3f3ff99..8a0a371 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
@@ -441,7 +441,7 @@
 
 UseNullptrCheck::UseNullptrCheck(StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
-      NullMacrosStr(Options.get("NullMacros", "NULL")) {
+      NullMacrosStr(Options.get("NullMacros", "")) {
   StringRef(NullMacrosStr).split(NullMacros, ",");
 }