Вы пытались указать [nzAllowClear] компонента nz-select? Также проверьте, что элемент управления имеет controlName в реактивной форме
There's a list of Haml implementations on the Wikipedia page. At the moment, there isn't one for Java.
There has been a Java implementation for a few years now : https://github.com/raymyers/JHaml
HAML is dependent on Ruby. I know there is a Python clone of HAML, not sure about Java.
Although, SASS/Compass are language agnostic.