I think, that's why we have to use ignore script variable with onStart() script to skip the entire transformation.


ignoreFlagA boolean variable ("true" or "false") where true in onStart scripts will cause the entire transformation process to be skipped. Setting it to true in onBefore scripts will cause the current row transformation to be skipped, and will continue to process the remaining rows. Default is "false".
if (source.u_user_name.nil()){ ignore = true; }