Fix broken subject default in crashmailbatch (#109)

* Fix broken subject default in crashmailbatch

* still use get for safety

Co-authored-by: Joe Portela <joe@resy.com>

superlance/crashmailbatch.py

@@ -60,8 +60,8 @@ class CrashMailBatch(ProcessStateEmailMonitor):
     process_state_events = ['PROCESS_STATE_EXITED']
 
     def __init__(self, **kwargs):
-        kwargs['subject'] = kwargs.get('subject',
-                                       'Crash alert from supervisord')
+        if kwargs.get('subject') is None:
+            kwargs['subject'] = 'Crash alert from supervisord'
         ProcessStateEmailMonitor.__init__(self, **kwargs)
         self.now = kwargs.get('now', None)