NEXT. JS. 7. Assigning an issue to user

getting this error:
A <Select.Item /> must have a value prop that is not an empty string. This is because the Select value can be set to an empty string to clear the selection and show the placeholder.

  <Select.Item value="">Unassigned</Select.Item>

i dont this correct way or not
able to fix by adding this code

   axios.patch(`/api/issues/${}`, {
          assignedToUserId: userId === 'null' ? null : userId,

 <Select.Item value="null">Unassigned</Select.Item>```