Fixed #1107 min-height when the ui-dropdown-item have a null label.
min-height: 1em is the best way, because "em" is "Relative to the font-size of the element (2em means 2 times the size of the current font)"
The same solution has applied on select2 in the past select2/select2@4530e74
Fixed #1107 - Min height when label is null
This looks a bit weird to me, I'll use the same approach we had for ui-dropdown-label-empty instead.
Fixed via #1626