unsupported operand type(s) for +=: 'int' and 'NoneType'

[gminog]

Under certain circumstances, the event argument passed in the functions 'append' or 'append_middle' of the RuleTypes class can be None.
The aforementioned functions now perform a None check so that errors such as the below are avoided:

ERROR:root:Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/elastalert/elastalert.py", line 1269, in handle_rule_execution
    num_matches = self.run_rule(rule, endtime, rule.get('initial_starttime'))
  File "/usr/lib/python3.6/site-packages/elastalert/elastalert.py", line 897, in run_rule
    self.run_query(rule, tmp_endtime, endtime)
  File "/usr/lib/python3.6/site-packages/elastalert/elastalert.py", line 649, in run_query
    rule_inst.add_aggregation_data(data)
  File "/usr/lib/python3.6/site-packages/elastalert/ruletypes.py", line 1144, in add_aggregation_data
    self.handle_event(event, agg_value, 'all')
  File "/usr/lib/python3.6/site-packages/elastalert/ruletypes.py", line 448, in handle_event
    self.cur_windows[qk].append((event, count))
  File "/usr/lib/python3.6/site-packages/elastalert/ruletypes.py", line 321, in append
    self.running_count += event[1]
TypeError: unsupported operand type(s) for +=: 'int' and 'NoneType'

ERROR:root:Uncaught exception running rule /opt/elastalert/rules/SpikeRule12: unsupported operand type(s) for +=: 'int' and 'NoneType'

@Qmando FYI