ara_m: Permit encoding of empty AID (--aid '') in ARA-M rules

Encoding an empty AID-REF-DO (4F) is neccessary to achieve the meaning
described in "Secure Element Access Control - Public Release v1.0"
Table 6-1: "Empty: Indicates that the rules to be stored or retrieved
are associated with all SE applications not covered by a specific rule".

Change-Id: Iac6c3d78bc9ce36bac47589e5f7a0cc78e2efc38

pySim/ara_m.py

@@ -348,7 +348,7 @@ class ADF_ARAM(CardADF):
             """Perform STORE DATA [Command-Store-REF-AR-DO] to store a (new) access rule."""
             # REF
             ref_do_content = []
-            if opts.aid:
+            if opts.aid != None:
                 ref_do_content += [{'aid_ref_do': opts.aid}]
             elif opts.aid_empty:
                 ref_do_content += [{'aid_ref_empty_do': None}]