Cannot start Plinth when apache2 is not installed

If I try to run Plinth when apache2 is not installed, I get this error:

File "/usr/local/lib/python3.4/dist-packages/Plinth-0.7.2-py3.4.egg/plinth/module_loader.py", line 129, in _initialize_module
    init()
  File "/usr/local/lib/python3.4/dist-packages/Plinth-0.7.2-py3.4.egg/plinth/modules/shaarli/__init__.py", line 43, in init
    is_external=True, enabled=is_enabled())
  File "/usr/local/lib/python3.4/dist-packages/Plinth-0.7.2-py3.4.egg/plinth/modules/shaarli/__init__.py", line 48, in is_enabled
    return action_utils.webserver_is_enabled('shaarli')
  File "/usr/local/lib/python3.4/dist-packages/Plinth-0.7.2-py3.4.egg/plinth/action_utils.py", line 92, in webserver_is_enabled
    stderr=subprocess.STDOUT)
  File "/usr/lib/python3.4/subprocess.py", line 607, in check_output
    with Popen(*popenargs, stdout=PIPE, **kwargs) as process:
  File "/usr/lib/python3.4/subprocess.py", line 859, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1463, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'a2query'

Since Apache2 is not a requirement for Plinth, Plinth should handle this exception and continue its startup.