Switch NULL to C++11 nullptr in source/Interpreter

Patch by Robert Matusewicz

llvm-svn: 206711
diff --git a/lldb/source/Interpreter/OptionValueEnumeration.cpp b/lldb/source/Interpreter/OptionValueEnumeration.cpp
index f282235..7aceac9 100644
--- a/lldb/source/Interpreter/OptionValueEnumeration.cpp
+++ b/lldb/source/Interpreter/OptionValueEnumeration.cpp
@@ -113,7 +113,7 @@
     m_enumerations.Clear();
     if (enumerators)
     {
-        for (size_t i=0; enumerators[i].string_value != NULL; ++i)
+        for (size_t i=0; enumerators[i].string_value != nullptr; ++i)
         {
             ConstString const_enumerator_name(enumerators[i].string_value);
             EnumeratorInfo enumerator_info = { enumerators[i].value, enumerators[i].usage };