Macro quoted string syntax (consecutive commas)

[_Grove_]

What is the function of the double commas (,,) in the code below?

data dm6a;
    set rawdata.dob rawdata.xds(where=(datc^=''));
    length pendtc $19.;
    if datc^= '' then do; %dtc(datc,,pendtc); end;
    else if visdatc ^= '' then do; %dtc(visdatc,,pendtc); end;
    else do; %dtc(visdatc,,pendtc); end;
run;

[Astounding · Accepted solution]

The commas indicate that when %DTC was defined, it was designed to hold three parameters.  When calling the macro, the values supplied are:

1st parameter = datc (or visdatc)

2nd parameter = (null string)

3rd parameter = pendtc

The extra comma holds the parameters in place.  Without it, macro language would think that the second parameter should be pendtc