It seems that you don't get a value for a operation parameter in case of drilling operations.
You will have to check if $value is equal to "--" and skip formatting in this case.
The error tells you in which procedure and in which file you have problems, it even displays the line of Tcl code you have problems with.
You just have to open the mentioned file search for the procedure and then check the line of Tcl code, to get an idea of what went wrong.
The check fails because you are checking a non-existent value. Remember that not all operations support all values.
In addition double-dash has a special meaning to many Tcl functions, so don't use it to indicate that a value is non-existent.
