Pay attention to "Changing"

data l_ct_imseg type vsep_t_imseg.
  refresh l_ct_imseg.
  append lines of ct_imseg to l_ct_imseg.
  call function 'HU_CREATE_GOODS_MOVEMENT'
   exporting
     if_event             = if_event
     if_simulate          = if_simulate
     if_commit            = if_commit
     if_tcode             = if_tcode
     is_imkpf             = is_imkpf
     it_move_to           = it_move_to
     it_internal_id       = it_internal_id
     it_external_id       = it_external_id
   importing
     ef_posted            = ef_posted
     es_message           = es_message
     et_messages          = et_messages
     es_emkpf             = es_emkpf
   changing
     ct_imseg             = l_ct_imseg
            .
    if l_ct_imseg is not initial.
      ct_imseg = l_ct_imseg.
    endif.