diff --git a/test/string_ref_test1.cpp b/test/string_ref_test1.cpp
index 261f6b0..b557230 100644
--- a/test/string_ref_test1.cpp
+++ b/test/string_ref_test1.cpp
@@ -102,6 +102,7 @@ int test_main( int , char* [] ) {
         interop ( *p, *p );
         test_substr ( *p );
         test_remove ( *p );
+        null_tests ( *p );
     
         p++;
         }