Combobox problem with blank item

Empty strings are not rendered by the browsers and measure 0,0. The list items in the combo box don’t have a minimum height because Wisej supports variable height items. You can either use the html symbol for non-breakable spaces &nsbp; or set the minimum height of list items in the theme or a mixin.

The min height value depends on your app the font, etc. I’d use 22 or use  

{
  "appearances": {
    "listitem": {
      "inherit": "listitem",
        "states": {
          "default": {
            "properties": {
                 "minHeight": 20
          }
        }
      }
    }
  }
}