PHP syntax Error - can not see where I have created this error

Question

while($row = mysqli_fetch_array($result)) {

    $op .= "<STRONG>" . $row[$fld1] . " > " . $row[$fld2] . "</STRONG>" . NL;
    if (!empty($row[$fld3]) ) 
         { $op .= $row[$fld3] . NL;}

}

---

ERROR GIVEN by Visual Studio Code, but also errors in runtime

syntax error, unexpected ')', expecting ']'

Help : I can not see where my error is - all brackets seem to be paired correctly.

I am testing for an empty value from a mysql query and therefore not printing its line

NL is a define for