If statement

I am new to Icon, so this is most certainly my fault, but I am not 
understanding where to go from here. I have a rather contorted matching 
function that takes a variable number of arguments. It's not necessary 
to go into that. Here is what I would like to accomplish:

if (a is null OR a == data[1])
        AND (b is null OR b == data[2])
        AND (c is null OR c == data[3])
  then return index

So, if the user supplies a, it's matched, otherwise, it skips that 
match. So on for b and c. Here is my real Icon code:

every idx := startAt to *spec do {
   if (/loopName | loopName == spec[idx][1]) & 
         (/segName | segName == spec[idx][2]) &
         ( /segMod | segMod == spec[idx][3]) then     return idx
}

When my function runs, I get this:

Run-time error 103
File edispec.icn; Line 14
string expected
offending value: &null
Traceback:
main()
testX096() from line 24 in edispec.icn
position_of(list_485 = 
[list_1(3),list_2(3),list_3(3),...,list_482(3),list_483(3),list_484(3)],1
,"CLM",&null,&null) from line 7 in edispec.icn
{&null == ""} from line 14 in edispec.icn

Now, I decided to break this down and figure out exactly where the error 
is happening and in the process I now have:

every idx := startAt to *spec do {
   if /loopName | loopName == spec[idx][1] then
      if /segName | segName == spec[idx][2] then
         if /segMod | segMod == spec[idx][3] then
            return idx
}

The above code works just as I would expect it to. With this code about 
30 unit tests pass just fine, the other code, 30 unit tests fails.

So, my question is what is wrong with my first if statement?

Thank you,

Jeremy