cgreen: Trying to mock multiple functions with the is_not_null constraint does not work

I’m using Ubuntu 20.04 with GCC 9.3.0-10ubuntu2 and clang 10.0.0-4ubuntu1 (the issue can be reproduced with both compilers), with cgreen compiled from source from commit 34cd1b6 - Extract common "discover_tests" function from the master branch.

The problem is that setting two different is_not_null constraints for different functions makes cgreen think that both functions should define that particular parameter. For lack of a better description I have a minimal sample with which I can reproduce this:

#include <cgreen/cgreen.h>
#include <cgreen/mocks.h>

Describe(test);
BeforeEach(test) {}
AfterEach(test) {}

void first_mock(int a, int *a_out)
{
    mock(a, a_out);
}

void second_mock(int b, int *b_out)
{
    mock(b, b_out);
}

int tested_func(int a, int b)
{
    int a_out, b_out;
    first_mock(a, &a_out); 
    second_mock(b, &b_out);
    return a_out + b_out;
}

Ensure(test, does_the_thing)
{
    int a_out_val = 10;
    int b_out_val = 20;

    expect(first_mock, 
        when(a_out, is_not_null),
        will_set_contents_of_parameter(a_out, &a_out_val, sizeof(a_out_val)));
    expect(second_mock, 
        when(b_out, is_not_null),
        will_set_contents_of_parameter(b_out, &b_out_val, sizeof(b_out_val)));

    assert_that(tested_func(1, 2), is_equal_to(30));
}

int main(void)
{
    TestSuite *suite = create_test_suite();
    add_test_with_context(suite, test, does_the_thing);
    return run_test_suite(suite, create_text_reporter());
}

Compiled with:

gcc test.c /usr/local/lib/libcgreen.so -o test

When run this gives the following output:

$ ./test
Running "main" (1 test)...
test.c:31: Failure: does_the_thing
        Mocked function [first_mock] did not define a parameter named [b_out]. Did you misspell it in the expectation or forget it in the mock's argument list?

test.c:38: Failure: does_the_thing
        Expected [tested_func(1, 2)] to [equal] [30]
                actual value:                   [262849778]
                expected value:                 [30]

  "main": 1 pass, 2 failures in 1ms.
Completed "main": 1 pass, 2 failures in 1ms.

If I remove when(a_out, is_not_null) or when(b_out, is_not_null),, or if I rename the parameter to have the same name in both cases it seems to work as intended:

$ ./test
Running "main" (1 test)...
  "main": 2 passes in 0ms.