### Summary

When using the user module to modify password_expire_min=0, the processing result does not meet expectations .
I guess the problem is caused by the following code in the user module.
```
    # deal with password expire min
    if user.password_expire_min:
        if user.user_exists():
            (rc, out, err) = user.set_password_expire_min()
```
Modifying to the following  code may fix this problem.
```
    # deal with password expire min
    if user.password_expire_min is not None:
        if user.user_exists():
            (rc, out, err) = user.set_password_expire_min()
```

### Issue Type

Bug Report

### Component Name

user

### Ansible Version

```console
$ ansible --version
ansible [core 2.11.1] 
  config file = None
  configured module search path = ['/home/betadmin/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /app/python3/lib/python3.8/site-packages/ansible
  ansible collection location = /home/betadmin/.ansible/collections:/usr/share/ansible/collections
  executable location = /app/python3/bin/ansible
  python version = 3.8.5 (default, Sep 18 2020, 14:55:53) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)]
  jinja version = 2.11.2
  libyaml = False
```


### Configuration

```console
$ ansible-config dump --only-changed
```


### OS / Environment

RHEL 7.4

### Steps to Reproduce

- name: Edit password_expire_min
  user:
    name: test
    password_expire_min: 0



### Expected Results

Minimum number of days between password change	: 0


### Actual Results


Minimum number of days between password change	: 2


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
"""
    This is a Darwin macOS User manipulation class.
    Main differences are that Darwin:-
      - Handles accounts in a database managed by dscl(1)
      - Has no useradd/groupadd
      - Does not create home directories
      - User password must be cleartext
      - UID must be given
      - System users must ben under 500
    This overrides the following methods from the generic class:-
      - user_exists()
      - create_user()
      - remove_user()
      - modify_user()
    """
    platform = 'Darwin'
    distribution = None
    SHADOWFILE = None
    dscl_directory = '.'
    fields = [
        ('comment', 'RealName'),
        ('home', 'NFSHomeDirectory'),
        ('shell', 'UserShell'),
        ('uid', 'UniqueID'),
        ('group', 'PrimaryGroupID'),
        ('hidden', 'IsHidden'),
    ]
    def __init__(self, module):