Automatically Press Select All Based on Selector Filter Value

Hi I have created 2 selectors in material wizard 1 screen (AM300010) as below

If the selector gives one record after putting the production number in the filter it should automatically press the Select All button.

How can I achieve this, I have tried using  Base.Actions["SelectAll"].Press(); but i get the error:

System.NullReferenceException
Message: Object reference not set to an instance of an object.

using System;
using PX.Data;
using System.Collections.Generic;
using PX.Objects.CS;
using System.Collections;
using System.Linq;
using PX.Objects.IN;
using PX.Objects.AM.Attributes;
using PX.Objects;
using PX.Objects.AM;

namespace PX.Objects.AM
{
  public class MatlWizard1_Extension : PXGraphExtension<PX.Objects.AM.MatlWizard1>
  {
    #region Event Handlers  

    protected void AMProdItem_Selected_FieldUpdated(PXCache cache, PXFieldUpdatedEventArgs e, PXFieldUpdated baseHandler)
    {

baseHandler?.Invoke(cache, e);
            var row = (AMProdItem)e.Row;
             if (row.Selected == true) // Only if the item is selected
        {
            //row.QtytoProd = 1.0000m;
          //cache.Update(row);
          cache.SetValueExt<AMProdItem.qtytoProd>(row, 1.0000m); // Notify Acumatica of the update
        }

    }

     #endregion

#region View Extensions


       public override void Initialize()
        {
            base.Initialize();

            Base.OpenOrders.SetProcessDelegate(list =>
            {
                var filter = Base.filter.Current;
                if (filter != null)
                {
                    var filterExt = filter.GetExtension<WizFilterExt>();

                    // Apply warehouse filter
                    if (filterExt?.UsrWarehouseSelector2 != null)
                    {
                        var warehouseID = filterExt.UsrWarehouseSelector2;
                        list = list.Where(item => item.SiteID == warehouseID).ToList();
                    }

                    // Apply production number filter
                    if (!string.IsNullOrWhiteSpace(filterExt?.UsrProdOrderNoFilter))
                    {
                        list = list.Where(item =>
                            item.ProdOrdID != null &&
                            item.ProdOrdID.Trim().Contains(filterExt.UsrProdOrderNoFilter.Trim())
                        ).ToList();
                    }

                     // If only one record is found, automatically select it
                   // if (list.Count == 1)
                   // {
                      // Execute the SelectAll action
                       // Base.selectall.Press();
                       // foreach (AMProdItem item in list)
                       // {
                        //    item.Selected = true;
                       //     Base.OpenOrders.Cache.SetValueExt<AMProdItem.qtytoProd>(item, 1.0000m);
                     //   }
                          // Press the "Select All" button programmatically
              //  Base.Actions["SelectAll"].Press(); // 
                  //  }             

                }                 

                MatlWizard1.FillMatlWrk(list, filter);
            });
        }

        protected virtual IEnumerable openOrders()
        {
            var baseView = new PXView(Base, true, Base.OpenOrders.View.BqlSelect);
            var startRow = PXView.StartRow;
            int totalRows = 0;
            var filter = Base.filter.Current;

            if (filter == null)
            {
                return baseView.Select(PXView.Currents, PXView.Parameters,
                    PXView.Searches, PXView.SortColumns, PXView.Descendings,
                    PXView.Filters, ref startRow, PXView.MaximumRows, ref totalRows);
            }

            var filterExt = filter.GetExtension<WizFilterExt>();

            // If neither filter is set, return base view
            if (filterExt?.UsrWarehouseSelector2 == null &&
                string.IsNullOrWhiteSpace(filterExt?.UsrProdOrderNoFilter))
            {
                return baseView.Select(PXView.Currents, PXView.Parameters,
                    PXView.Searches, PXView.SortColumns, PXView.Descendings,
                    PXView.Filters, ref startRow, PXView.MaximumRows, ref totalRows);
            }

            // Build the where clause based on active filters
            BqlCommand cmd = new Select<AMProdItem>();

            // Base conditions
            cmd = cmd.WhereAnd<Where<AMProdItem.function, NotEqual<OrderTypeFunction.disassemble>,
                And<Where<AMProdItem.isOpen, Equal<True>,
                And<AMProdItem.completed, NotEqual<True>>>>>>();

            // Add warehouse filter if specified
            if (filterExt?.UsrWarehouseSelector2 != null)
            {
                cmd = cmd.WhereAnd<Where<AMProdItem.siteID, Equal<Required<AMProdItem.siteID>>>>();
            }

            // Add production number filter if specified
            if (!string.IsNullOrWhiteSpace(filterExt?.UsrProdOrderNoFilter))
            {
                cmd = cmd.WhereAnd<Where<AMProdItem.prodOrdID, Like<Required<AMProdItem.prodOrdID>>>>();
            }

            var view = new PXView(Base, true, cmd);
            var parameters = new List<object>();

            // Add parameter values in the same order as the where conditions
            if (filterExt?.UsrWarehouseSelector2 != null)
            {
                parameters.Add(filterExt.UsrWarehouseSelector2);
            }
            if (!string.IsNullOrWhiteSpace(filterExt?.UsrProdOrderNoFilter))
            {
                parameters.Add("%" + filterExt.UsrProdOrderNoFilter + "%");
            }

            return view.Select(PXView.Currents, parameters.ToArray(),
                PXView.Searches, PXView.SortColumns, PXView.Descendings,
                PXView.Filters, ref startRow, PXView.MaximumRows, ref totalRows);

             // var result = view.Select(PXView.Currents, parameters.ToArray(),
              //  PXView.Searches, PXView.SortColumns, PXView.Descendings,
              //  PXView.Filters, ref startRow, PXView.MaximumRows, ref totalRows);

                // If only one record is returned, ensure it's selected

            //if (result.Count == 1)
            //{
           //    Base.Actions["SelectAll"].Press();
           // }

           // return result;

        }
    #endregion
  }
}

Thank you!