If record_name="" write empty value to dns made easy

This is necessary for instance when setting MX records on the root of a domain.
This is different than leaving record_name out completely which has the same
behaviour as before

lib/ansible/modules/extras/network/dnsmadeeasy.py

@@ -264,7 +264,7 @@ def main():
     record_name = module.params["record_name"]
 
     # Follow Keyword Controlled Behavior
-    if not record_name:
+    if record_name is None:
         domain_records = DME.getRecords()
         if not domain_records:
             module.fail_json(