Describe the bug
In the YearPicker (showYearPicker) of ReactDatePicker, pressing the Enter key does not select a year when the initial selected value is null or undefined.

However, mouse interaction works correctly and allows selecting a year even when no initial value is set.

This behavior is inconsistent with:

• Default DatePicker (day picker)
• MonthPicker

where keyboard selection works regardless of the initial selected value.

To Reproduce

const Default = () => {
  const [selectedDate, setSelectedDate] = useState<Date | null>(null);

  const handleChange = (date: Date | null) => {
    setSelectedDate(date);
  };

  return (
    <DatePicker
      selected={selectedDate}
      onChange={handleChange}
      showYearPicker
    />
  );
};

render(Default);

Steps:

1. Open the DatePicker
2. Navigate between years using arrow keys
3. Press Enter

Expected behavior

• Pressing Enter should select the currently focused year
• Behavior should be consistent with mouse interaction and other picker modes
• Selection should work even when selected is initially null

Actual behavior

• Pressing Enter does nothing when selected is null
• Year is not selected
• onChange / onSelect is not triggered

Root Cause

In src/year.tsx:

case KeyType.Enter:
  if (this.props.selected == null) {
    break;
  }

This early exit prevents selection when selected is null.

Additional context

• There is an existing test enforcing this behavior:

  • Prevents onSelect from being called when selected is null

• This behavior appears unintended and inconsistent with other pickers

• Likely introduced for test coverage rather than UX correctness

Suggested fix

• Remove the selected == null guard for Enter key handling
• Allow selection based on the currently focused/preselected year
• Update/remove the corresponding test enforcing the incorrect behavior