Fix missing NULL check in MPI
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 7908f91..56817cc 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -1,3 +1,6 @@
+Arguments with no value
+mpi_null:
+
 Base test mpi_read_write_string #1
 mpi_read_write_string:10:"128":10:"128":100:0:0