fix: do not serialize empty lists in ec2 (#4639)

Author: kuhe

.changes/next-release/bugfix-EC2-de915a43.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "EC2",
+  "description": "do not serialize empty lists for EC2"
+}

lib/query/query_param_serializer.js

@@ -42,7 +42,9 @@ function serializeList(name, list, rules, fn) {
   var memberRules = rules.member || {};
 
   if (list.length === 0) {
-    fn.call(this, name, null);
+    if (rules.api.protocol !== 'ec2') {
+      fn.call(this, name, null);
+    }
     return;
   }