Postman variable returning incorrect value

in the test for a Get by Id request I am doing this on an int? datatype property:
var r = pm.response.json();
pm.environment.set(‚ÄúinitialValue‚ÄĚ, r.positionTypeID);

often r.positionTypeID returns null:
{
…
‚ÄúpositionTypeID‚ÄĚ : null
…
}

in a Patch request:
{
…
‚ÄúpositionTypeID‚ÄĚ: {{initialValue}},
…
}

my request fails because the patch request is:
{
…
‚ÄúpositionTypeID‚ÄĚ: ‚Äú‚ÄĚ,
…
}

instead of ‚ÄúpositionTypeID‚ÄĚ: null,

How do I get the variable ‚ÄúpositionTypeID‚ÄĚ to return null instead of ‚Äú‚ÄĚ?