How to send empty arguments in a parametrized pytest test?

I am using Pytest. I have a function with several arguments and I am using a parametrized test to check different combinations of those arguments. But I would like to be able to not have all arguments in all test cases. Is there a way that I can indicate in the tuples where I define the test cases that some arguments are empty?

Here is a minimal example. In the case below I would like to have another test wher I pass only the first argument, e.g. 1 and the expected result 5 (1+4).

I have tried (1,,5) and (1,None,5) but none seems to work.

The example below is a very simplified case, I could probably have a separate test function. But in a general case with lots of arguments it would be quite helpful to be able to parametrize the function to test not passing a each argument.

import pytest

def foo(arg1, arg2=4):
    return arg1+arg2

@pytest.mark.parametrize("first,second,expected_result",[(1,2,3),(2,3,5)])
def test(first,second,expected_result):
    assert foo(first,second) == expected_result

A simple approach is:

@pytest.mark.parametrize(
    "first,second,expected_result", [(1, 2, 3), (2, 3, 5), (1, None, 5)]
)
def test(first, second, expected_result):
    if second is None:
        actual = foo(first)
    else:
        actual = foo(first, second)
    assert actual == expected_result

A more generic approach, which can be used to test any function with any number of parameters:

@pytest.mark.parametrize(
    "args,kwargs,expected_result",
    [
        ((1, 2), {}, 3),
        ((2, 3), {}, 5),
        ((1,), {}, 5),
    ],
)
def test(args, kwargs, expected_result):
    actual = foo(*args, **kwargs)
    assert actual == expected_result