--- policycoreutils-extra/scripts/rlpkg
+++ policycoreutils-extra/scripts/rlpkg
@@ -90,6 +90,9 @@
 
 def find_installed_packages(search_key):
     """Returns a list of Package objects that matched the search key."""
+    if not isinstance(search_key, str) or not search_key.strip():
+        raise ValueError("search_key may not be an empty string")
+
     try:
         t = portage.db["/"]["vartree"].dbapi.match(search_key)
     # catch the "amgigous package" Exception