json legend request with scale param fails when categorize is used for a mark size

GeoServer GeoServer User
1

With Geoserver 2.27.2 I’m trying to create an sld for a point layer, with a circle mark with a dynamic size using the categorize function. The layer source column I intend to use to determine the appropriate size is of a float type (doesn’t matter if postgresql or a shape file). It contains no null or 0 values. If the style looks like below then the legend is ok as a png, not as json.

So this works
wms?service=WMS&version=1.1.0&request=GetLegendGraphic&layer=demoshape&format=image/png&scale=400
while this does not:
wms?service=WMS&version=1.1.0&request=GetLegendGraphic&layer=demoshape&format=application/json&scale=400

The exception is:

java.lang.NullPointerException: ECQL does not support null literal value

<?xml version="1.0" encoding="ISO-8859-1"?>
<StyledLayerDescriptor version="1.0.0"
  xsi:schemaLocation="http://www.opengis.net/sld StyledLayerDescriptor.xsd"
  xmlns="http://www.opengis.net/sld"
  xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <NamedLayer>
    <Name>Simple Point</Name>
    <UserStyle>
      <Title>Demo style</Title>
      <FeatureTypeStyle>
        <Rule>
          <PointSymbolizer>
            <Graphic>
              <Mark>
                <WellKnownName>circle</WellKnownName>
                <Fill>
                  <CssParameter name="fill">#FF000B</CssParameter>
                </Fill>
              </Mark>
              <Size>
                <ogc:Function name="Categorize">
                  <ogc:PropertyName>flyttal</ogc:PropertyName>
                  <ogc:Literal>5</ogc:Literal>
                  <ogc:Literal>2</ogc:Literal>
                  <ogc:Literal>10</ogc:Literal>
                  <ogc:Literal>4</ogc:Literal>
                  <ogc:Literal>15</ogc:Literal>
                  <ogc:Literal>6</ogc:Literal>
                  <ogc:Literal>20</ogc:Literal>

                </ogc:Function>
              </Size>
            </Graphic>
          </PointSymbolizer>
        </Rule>
      </FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>

If I use categorize for the stroke-width property instead, like below, then the getlegendgraphic with a scale param for application/json works:

<?xml version="1.0" encoding="ISO-8859-1"?>
<StyledLayerDescriptor version="1.0.0"
  xsi:schemaLocation="http://www.opengis.net/sld StyledLayerDescriptor.xsd"
  xmlns="http://www.opengis.net/sld"
  xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <NamedLayer>
    <Name>Simple Point</Name>
    <UserStyle>
      <Title>Demo style</Title>
      <FeatureTypeStyle>
        <Rule>
          <PointSymbolizer>
            <Graphic>
              <Mark>
                <WellKnownName>circle</WellKnownName>
                <Fill>
                  <CssParameter name="fill">#FF000B</CssParameter>
                </Fill>
                <Stroke>
                  <CssParameter name="stroke">#D3D3D3</CssParameter>
                  <CssParameter name="stroke-width">
                    <ogc:Function name="Categorize">
                      <ogc:PropertyName>flyttal</ogc:PropertyName>
                      <ogc:Literal>5</ogc:Literal>
                      <ogc:Literal>2</ogc:Literal>
                      <ogc:Literal>10</ogc:Literal>
                      <ogc:Literal>4</ogc:Literal>
                      <ogc:Literal>15</ogc:Literal>
                      <ogc:Literal>6</ogc:Literal>
                      <ogc:Literal>20</ogc:Literal>
                    </ogc:Function>
                  </CssParameter>
                </Stroke>
              </Mark>
              <Size>
                4
              </Size>
            </Graphic>
          </PointSymbolizer>
        </Rule>
      </FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>

If the scale param is omitted from the getlegendgraphic call then it always succeeds (and note that the style isn’t scale variable)

Is this a known issue (or am I doing something wrong)?

Edit.
interpolate similarly configured doesn’t have the same issue (for my specific usecase involving around 100k points it doesn’t appear fast enough, but that’s beside the point)