MPS Reader Tests: Test feed() of NULL buffer

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/tests/suites/test_suite_mps.data b/tests/suites/test_suite_mps.data
index a1a6e5c..158302b 100644
--- a/tests/suites/test_suite_mps.data
+++ b/tests/suites/test_suite_mps.data
@@ -117,3 +117,6 @@
 
 MPS Reader: Pausing, inconsistent continuation, #8
 mbedtls_reader_inconsistent_usage:8
+
+MPS Reader: Feed with invalid buffer (NULL)
+mbedtls_mps_reader_feed_empty:0