Problem with IS NULL condition in GeoServer CSS style

Question

I have a style that divide features in PostGIS layer to four categories based on atributte Z_KAT. In the fourth category I want to specify that Z_KAT is equal to '04' OR null value.

Condition for text value '04' works well but condition for null value doesn't work (only selected features with value '04'). In SLD it works well so I can compare the result in "layer preview" but i need the style in CSS.

I also tried something like this: Problem with NotEqualTo filters in SLD and CSS but without success.

How can I get this to work?

Version of GeoServer and CSS extension is 2.16.2.

Here is my code:

/* @title Vodní nádrž I. kategorie TBD*/
[Z_KAT='01']{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #ff0000;
  }
}

/* @title Vodní nádrž II. kategorie TBD*/
[Z_KAT='02']{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #008080;
  }
}

/* @title Vodní nádrž III. kategorie TBD*/
[Z_KAT='03']{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #00ffff;
  }
}

/* @title Vodní nádrž IV. kategorie TBD*/
[Z_KAT='04'],[Z_KAT is Null]{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #0000ff;
  }
}

Answer 1

After many attemps I solved the problem!

I added translation mode to flat that translate CSS rules to SLD almost in 1:1. (The Flat translation mode)

Then I adjusted the conditions in my code to match my categories like this:

@mode "Flat";

/* @title Vodní nádrž I. kategorie TBD*/
[Z_KAT='01']{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #ff0000;
  }
}

/* @title Vodní nádrž II. kategorie TBD*/
[Z_KAT='02']{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #008080;
  }
}

/* @title Vodní nádrž III. kategorie TBD*/
[Z_KAT='03']{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #00ffff;
  }
}

/* @title Vodní nádrž IV. kategorie TBD*/
[Z_KAT not in ('01','02','03')],[Z_KAT is Null]{
  mark: symbol(square);
  mark-size: 7;
  mark-rotation: 45;
  :mark{
    fill: #0000ff;
  }
}

Now the null values are correctly selected and the legend contains the correct categories.