### Summary

https://docs.ansible.com/ansible/latest/collections/ansible/builtin/mandatory_filter.html makes no mention of the `msg` argument that was introduced in 0e7e3c0ae89a70c386168827b0c9defb956bee7e

### Issue Type

Documentation Report

### Component Name

lib/ansible/plugins/filter/mandatory.yml

### Ansible Version

```console
n/a
```


### Configuration

```console
n/a
```


### OS / Environment

n/a

### Additional Information

n/a

### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
uuid_namespace = namespace
    if not isinstance(uuid_namespace, uuid.UUID):
        try:
            uuid_namespace = uuid.UUID(namespace)
        except (AttributeError, ValueError) as e:
            raise AnsibleFilterError("Invalid value '%s' for 'namespace': %s" % (to_native(namespace), to_native(e)))
    
    return to_text(uuid.uuid5(uuid_namespace, to_native(string, errors='surrogate_or_strict')))
def mandatory(a, msg=None):
    """Make a variable mandatory."""
    from jinja2.runtime import Undefined
    if isinstance(a, Undefined):
        if a._undefined_name is not None:
            name = "'%s' " % to_text(a._undefined_name)
        else:
            name = ''
        if msg is not None:
            raise AnsibleFilterError(to_native(msg))
        else:
            raise AnsibleFilterError("Mandatory variable %s not defined." % name)
    return a
def combine(*terms, **kwargs):