Hide the "- none -" option

When using a radio button field in a priceset, CiviCRM automatically adds a '- none -' option (unless the field is required, but it should not be, since the donor can also enter an amount in the Other Amount field).

It's possible to hide it with CSS, but the extension should do it automatically.

Example CSS:

.crm-contribution-page-id-34 #priceset .contribution_amount-content .price-set-row:last-child {
  display: none;
}

Where id-34 is the contribution form ID.