API: inv_lot_api_pub.update_inv_lot has return status as NULL

hi Everyone,

We have a requirement to update the lot expiry date. The API: 'inv_lot_api_pub.update_inv_lot' updates the lot expiry date as expected, but it is giving return status as NULL. Can you please help me understand why is this happening? Below is the sample code used:

  declare

    lr_lot_rec                  mtl_lot_numbers%rowtype := NULL;

    lrx_lot_rec                 mtl_lot_numbers%rowtype := NULL;

    x_object_id                 NUMBER;

    ln_message_count            NUMBER                           := 0;

    lc_message_list             VARCHAR2 (4000)                  := NULL;

    lc_return_status            VARCHAR2 (1)                     := 'S';

    ln_msg_index_out            NUMBER                           := 0;

    ld_expiry_date              DATE                             := NULL;

  begin

  lc_message_list  := null;