Map.get(key, defaultvalue) doesn't work properly if current value is null.

I have a Map, args, which contains a key/value pair 'abcd':null .
I create an default object and then do the get:

def default_abcd = new abcd(blah, blah)
args.get('freq',default_freq)

Now the value of args.abcd is the new object. However, since the key 'abcd' previously existed and had a value (null), the get() call should have left the value alone (as null).