diff --git a/api.lua b/api.lua
index 7ca1b0a..f064657 100644
--- a/api.lua
+++ b/api.lua
@@ -141,6 +141,9 @@ function classroom.get_students_by_selector(selector)
 end
 
 function classroom.run_action(aname, runner, selector, params)
-	local action = _action_by_name[aname]
-	action.func(runner, classroom.get_students_by_selector(selector))
+	local action   = _action_by_name[aname]
+	local students = classroom.get_students_by_selector(selector)
+	if #students > 0 then
+		action.func(runner, students)
+	end
 end