Tried to reproduce bug with empty array

Tried to reproduce bug with empty array on master but got following traceback:
```
File "examples/django/rpctest/manage.py", line 43, in <module>
    execute_manager(settings)
  File "/ENV/lib/python2.7/site-packages/django/core/management/__init__.py", line 459, in execute_manager
    utility.execute()
  File "/ENV/lib/python2.7/site-packages/django/core/management/__init__.py", line 382, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/ENV/lib/python2.7/site-packages/django/core/management/commands/test.py", line 49, in run_from_argv
    super(Command, self).run_from_argv(argv)
  File "/ENV/lib/python2.7/site-packages/django/core/management/base.py", line 196, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/ENV/lib/python2.7/site-packages/django/core/management/base.py", line 232, in execute
    output = self.handle(*args, **options)
  File "/ENV/lib/python2.7/site-packages/django/core/management/commands/test.py", line 72, in handle
    failures = test_runner.run_tests(test_labels)
  File "/ENV/lib/python2.7/site-packages/django/test/simple.py", line 380, in run_tests
    suite = self.build_suite(test_labels, extra_tests)
  File "/ENV/lib/python2.7/site-packages/django/test/simple.py", line 267, in build_suite
    suite.addTest(build_suite(app))
  File "/ENV/lib/python2.7/site-packages/django/test/simple.py", line 79, in build_suite
    test_module = get_tests(app_module)
  File "/ENV/lib/python2.7/site-packages/django/test/simple.py", line 36, in get_tests
    test_module = import_module('.'.join(prefix + [TEST_MODULE]))
  File "/ENV/lib/python2.7/site-packages/django/utils/importlib.py", line 35, in import_module
    __import__(name)
  File "/home/srk/workspace/spyne/examples/django/rpctest/core/tests.py", line 30, in <module>
    from rpctest.core.views import app, hello_world_service, Container
  File "/home/srk/workspace/spyne/examples/django/rpctest/core/views.py", line 60, in <module>
    class ContainerService(ServiceBase):
  File "/home/srk/workspace/spyne/examples/django/rpctest/core/views.py", line 75, in ContainerService
    @rpc(_returns=Array(FieldContainer))
  File "/home/srk/workspace/spyne/spyne/model/complex.py", line 977, in __new__
    raise ValueError(serializer)
ValueError: None
```