New version of Docplex breaks QuadraticProgram

[t-imamichi]

Information

• Qiskit Optimization version: latest
• Python version: 3.8.7
• Operating system: macOS 11.2

What is the current behavior?

The latest version of Docplex breaks QuadraticProgram
https://pypi.org/project/docplex/2.20.204/

Steps to reproduce the problem

$ python -m unittest test/test_quadratic_program.py
E
======================================================================
ERROR: test_quadratic_program (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: test_quadratic_program
Traceback (most recent call last):
  File "/usr/local/Cellar/python@3.8/3.8.7_2/Frameworks/Python.framework/Versions/3.8/lib/python3.8/unittest/loader.py", line 154, in loadTestsFromName
    module = __import__(module_name)
  File "/Users/ima/tasks/1_2021/qiskit/opt/test/test_quadratic_program.py", line 23, in <module>
    from qiskit_optimization import INFINITY, QiskitOptimizationError, QuadraticProgram
  File "/Users/ima/tasks/1_2021/qiskit/opt/qiskit_optimization/__init__.py", line 88, in <module>
    from .problems.quadratic_program import QuadraticProgram
  File "/Users/ima/tasks/1_2021/qiskit/opt/qiskit_optimization/problems/__init__.py", line 54, in <module>
    from .quadratic_program import QuadraticProgram
  File "/Users/ima/tasks/1_2021/qiskit/opt/qiskit_optimization/problems/quadratic_program.py", line 27, in <module>
    from docplex.mp.linear import Var
ImportError: cannot import name 'Var' from 'docplex.mp.linear' (/Users/ima/envs/dev38/lib/python3.8/site-packages/docplex/mp/linear.py)


----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)

Details

Var was originally implemented as part of mp.linear until 2.15.194 (Jul 16, 2020). So we used it.
But, Var was moved to mp.dvar in 2.16.196 (Nov 9, 2020). mp.linear.Var was kept as an alias. So, Aqua works without change. There is no mention in the release note and no deprecation warning.
Finally, mp.linear.Var was removed in 2.20.204 (Feb 4, 2021). It caused the issue.

Reference:

• Release note: https://pypi.org/project/docplex/2.20.204/

What is the expected behavior?

The unit test passes

Suggested solutions

I will fix it.