GeoServer GetLegendGraphic without x-mark

Question

I'm using the GeoServer WMS to display some raster data with a custom color ramp. When I request a legend using GetLegendGraphic, I get a legend entry with a big red X in it:

Is there any way I can get a legend graphic with this X omitted? Here's my SLD:

  <sld:RasterSymbolizer>
    <sld:ColorMap>
      <sld:ColorMapEntry color="#ffffe5" opacity="0" quantity="0"/>
      <sld:ColorMapEntry color="#ffffe5" opacity="1" quantity="0"   label="0 mm"  />
      <sld:ColorMapEntry color="#f7fcb9" opacity="1" quantity="25"  label="25 mm" />
      <sld:ColorMapEntry color="#d9f0a3" opacity="1" quantity="50"  label="50 mm" />
      <sld:ColorMapEntry color="#addd8e" opacity="1" quantity="100" label="100 mm"/>
      <sld:ColorMapEntry color="#78c679" opacity="1" quantity="150" label="150 mm"/>
      <sld:ColorMapEntry color="#41ab5d" opacity="1" quantity="200" label="200 mm"/>
      <sld:ColorMapEntry color="#238443" opacity="1" quantity="250" label="250 mm"/>
      <sld:ColorMapEntry color="#006837" opacity="1" quantity="300" label="300 mm"/>
      <sld:ColorMapEntry color="#004529" opacity="1" quantity="400" label="400 mm"/>
    </sld:ColorMap>
    <sld:ContrastEnhancement/>
  </sld:RasterSymbolizer>

(The opacity=0 ColorMapEntry is there to prevent NODATA pixels from being displayed.)

Answer 1

That is representing your NODATA value, if you leave that out of the style there will be no X in the legend.

If it really bothers you then you could propose an enhancement to GeoServer's legend graphic code after you have read this guide.