How to prevent Flutter DropdownButton from returning route error before being clicked before it is loaded to widget tree?

Question

I am trying to recreate the navigational function from excel in Flutter Paginated table which allows you to move down multiple rows by holding enter. The table below:

Each cell has a button that when clicked replaces the button cell with either a TextFormField or a DropdownMenuButton as seen in the code below. I also change the focus node to the next column when a selection is made:

@override
  Widget build(BuildContext context) {
    RegisterProvider registerProvider = Provider.of<RegisterProvider>(context);

    LineItem item = widget.item;

    int index = item.index!;

    // Show the dropdown if this index is selected and return the dropdown button:
    if (registerProvider.selectedIndex == index &&
        registerProvider.selectedColumn == RegisterProvider.typeColumn) {
      // Get the focus node for the corresponding cell:  
      FocusNode node =
          registerProvider.focusNodes[RegisterProvider.typeColumn]![index];

      // Returns the dropdown to selected the type:
      return DropdownButton<String>(
        focusNode: node,
        value: item.type,
        items: LineItem.types.map<DropdownMenuItem<String>>((String value) {
          return DropdownMenuItem<String>(
            value: value,
            child: Text(value),
          );
        }).toList(),
        onChanged: (newType) {
          // print("Changed type");
          // bool res = registerProvider.changeIsDisabled();

          if (newType != null) {
            // Update the selected type: 
            item.type = newType;
            // The list of possible charges for the selected type:
            List<String> chargeSelection =
                LineItem.correspondingcharges[newType]!;
            // Set the charge as the first charge:
            item.charge = chargeSelection.first;
            // Set the pressure test:
            item.setWorkingPressure();
            // Determine if the new charge selection has only one value there is no need to move to the charge column:
            if (chargeSelection.length == 1) {
              // Update the selected column:
              registerProvider.selectedColumn = RegisterProvider.signageColumn;
              // This puts the cursor in the next dropdown button:
              registerProvider.focusNodes[registerProvider.selectedColumn]
                      ?[index]
                  .requestFocus();
              registerProvider.refresh();
            } else {
              // Update the selected column:
              registerProvider.selectedColumn = RegisterProvider.chargeColumn;

              registerProvider.refresh();
              // This puts the cursor in the next dropdownbutton input:
              registerProvider.focusNodes[RegisterProvider.chargeColumn]![index]
                  .requestFocus();
            }
          }
        },
      );
    }
    return InkWell(
      child: Padding(
        padding: const EdgeInsets.all(8.0),
        // Space to make the selection bigger:
        child: Text(
          item.type ?? 'Choose Type',
          style: TextStyle(color: item.type == null ? Colors.red : null),
        ),
      ),
      onTap: () {
        // Update the selected index:
        registerProvider.selectedIndex = index;
        // Update the selected column:
        registerProvider.selectedColumn = RegisterProvider.typeColumn;
        // Refresh the page:
        registerProvider.refresh();
        // This puts the cursor in the text field input:
        registerProvider.focusNodes[RegisterProvider.typeColumn]?[index]
            .requestFocus();
      },
    );
  }

I am trying to recreate the excel feature that allows the user to move down multiple rows by holding enter. When I try to hold enter I get this error:

══╡ EXCEPTION CAUGHT BY SERVICES LIBRARY ╞══════════════════════════════════════════════════════════ The following assertion was thrown while processing the key message handler: Assertion failed: file:///C:/src/flutter/packages/flutter/lib/src/material/dropdown.dart:1339:12 _dropdownRoute == null is not true

When the exception was thrown, this was the stack: dart-sdk/lib/internal/js_dev_runtime/private/ddc_runtime/errors.dart 294:3 throw dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 35:3 assertFailed packages/flutter/src/material/dropdown.dart 1339:27 [_handleTap] packages/flutter/src/material/ink_well.dart 845:21
activateOnIntent packages/flutter/src/widgets/actions.dart 597:39
invoke packages/flutter/src/widgets/actions.dart 338:16
[_invoke] packages/flutter/src/widgets/actions.dart 666:27
invokeActionIfEnabled packages/flutter/src/widgets/shortcuts.dart 851:81 handleKeypress packages/flutter/src/widgets/shortcuts.dart 1042:20
[_handleOnKey] ...

How can I prevent the dropdown from being selected if enter is held down?