AT function not working correction in v12

In attempting to use the AT function, we have found that the 3rd optional parameter does not work.

select at(' ','Test String',2) from system.iota;

That results in an error

select at(' ','Test String') from system.iota;

This works just fine.

Documentation shows:

AT( str1, str2[, start] )

Return integer location (1-based) of str1 in str2, with optional start starting point.

If str1 is not found in str2, 0 is returned.

Any idea of what is going on?

Thanks,

Chris