change curly brackets

                // Create pairs of controls (IgG) with target samples if they are supplied

                ch_bam_control_ctrlgrp.cross(ch_bam_target_ctrlgrp)

                    .map{

                      // row -> [row[1][1][0], row[1][1][1], row[0][1][1]]

                      row -> [row[0]]

                      row -> [row[1][1][0], row[1][1][1], row[0][1][1]]

                    }    

                    .set(ch_bam_paired)

                    .set{ch_bam_paired}

                //  // EXAMPLE CHANNEL STRUCT: [[META], TARGET_BAM, CONTROL_BAM]

                  ch_bam_paired | view