[EUI] Setting the value to undefined does not select the blank option.

[cnasikas]

A EuiSelect with hasNoInitialSelection creates a black option at the begging of the select. This is very useful when you don't want to preselect a value. If you select a value, and then you set it to undefined the black option is not selected. Example:

<EuiSelect
  fullWidth
  data-test-subj="subcategorySelect"
  hasNoInitialSelection
  options={subcategoriesOptions}
  value={subcategory ?? undefined}
  onChange={(e) => {// set the subcategory}}
/>

If I change value={subcategory ?? undefined} to value={subcategory ?? ''} (empty string) then the blank option is selected.

Steps to reproduce:

1. Select an option.
2. Make the value undefined. Example: You press a button that sets the value to undefined.

I think the component should handle both cases. Thanks!

[elasticmachine]

Pinging @elastic/eui-design (EUI)

[snide]

EuiSelect is just a regular HTML select in disguise. Regular selects do not allow undefined values. If you want one, you need to pass them as an empty option in your array and assign it. Read issue too quickly in the morning, but this is why it happens. It's actually an empty string in disguise. :)

[snide]

Sorry, I read this one too quickly. I forgot about the extra prop we add! It probably makes sense that it can handle both.