nested_subelements plugin doesn't work with Ansible 2.1

[Berkin Ozisikyilmaz]

The plugin has been written by
# (c) 2013, Serge van Ginderachter <serge@xxxx>
#
# This file is part of Ansible

It begins like this:

import ansible.utils as utils
import ansible.errors as errors


class LookupModule(object):

    def __init__(self, basedir=None, **kwargs):
        self.basedir = basedir


    def run(self, terms, inject=None, **kwargs):
        terms = utils.listify_lookup_plugin_terms(terms, self.basedir, inject)
        terms[0] = utils.listify_lookup_plugin_terms(terms[0], self.basedir, inject)

When running it in ansible 1.7, things work as expected.

While running it in ansbile 2.1,

An exception occurred during task execution. The full traceback is:
Traceback (most recent call last):
  File "/work/github/berkin/ansible-2.0/lib/ansible/executor/task_executor.py", line 91, in run
    items = self._get_loop_items()
  File "/work/github/berkin/ansible-2.0/lib/ansible/executor/task_executor.py", line 191, in _get_loop_items
    items = self._shared_loader_obj.lookup_loader.get(self._task.loop, loader=self._loader, templar=templar).run(terms=loop_terms, variables=self._job_vars)
AttributeError: 'NoneType' object has no attribute 'run'

fatal: [devtest]: FAILED! => {"failed": true, "msg": "Unexpected failure during module execution.", "stdout": ""}