Color interpolation sometimes fails

[moradology]

stack trace:

java.lang.IllegalArgumentException: step cannot be 0.
        at scala.collection.immutable.NumericRange$.count(NumericRange.scala:279)
        at scala.collection.immutable.NumericRange.numRangeElements$lzycompute(NumericRange.scala:52)
        at scala.collection.immutable.NumericRange.numRangeElements(NumericRange.scala:51)
        at scala.collection.immutable.NumericRange.length(NumericRange.scala:54)
        at scala.collection.immutable.NumericRange.foreach(NumericRange.scala:72)
        at scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:59)
        at scala.collection.mutable.ListBuffer.$plus$plus$eq(ListBuffer.scala:183)
        at geotrellis.server.ogc.Render$.linearInterpolationBreaks(Render.scala:40)
        at geotrellis.server.ogc.ColorRampStyle.renderImage(OgcStyle.scala:64)
        at geotrellis.server.ogc.Render$.apply(Render.scala:16)
        at geotrellis.server.ogc.wms.WmsView$$anonfun$responseFor$1$$anonfun$apply$5.apply(WmsView.scala:91)
        at geotrellis.server.ogc.wms.WmsView$$anonfun$responseFor$1$$anonfun$apply$5.apply(WmsView.scala:89)
        at cats.effect.internals.IORunLoop$.cats$effect$internals$IORunLoop$$loop(IORunLoop.scala:139)
        at cats.effect.internals.IORunLoop$RestartCallback.signal(IORunLoop.scala:351)
        at cats.effect.internals.IORunLoop$RestartCallback.run(IORunLoop.scala:362)
        at cats.effect.internals.Trampoline.cats$effect$internals$Trampoline$$immediateLoop(Trampoline.scala:70)
        at cats.effect.internals.Trampoline.startLoop(Trampoline.scala:36)
        at 

with conf:

	styles = [
            {
                name = "greyscale2"
                title = "Greyscale Ramp"
                type = "colorrampconf"
                colors = ${color-ramps.slope}
                min-render = 0
                max-render = 80
                stops = 255
            }
        ]
		
	"slope": [
        0x000000FF, 0xFFFFFFFF
    ] 

[jfbourgon]

The issue might be related to computed values from the layer since a similar configuration on another layer is not raising the exception:

slope = {
        type = "mapalgebrasourceconf"
        name = "slope"
        title = "Slope Map of High Resolution Digital Terrain Model generated from LiDAR"
        algebra = {
          "args" : [
            {
              "name" : "hrdtm",
              "symbol" : "rasterV"
            }
          ],
          "symbol" : "fslope"
        }
        defaultStyle = "default"
        styles = [
            {
                name = "greyscaleramp"
                title = "Greyscale Ramp"
                type = "colorrampconf"
                colors = ${color-ramps.slope}
                min-render = 0
                max-render = 90
                stops = 255
            },
            {
                name = "greyscalemap"
                title = "Greyscale Map"
                type = "colormapconf"
                color-map = ${color-maps.slope}
            }
        ]
    },
    hillshade = {
        type = "mapalgebrasourceconf"
        name = "hillshade"
        title = "Hillshade of High Resolution Digital Terrain Model generated from LiDAR"
        algebra = {
          "args" : [
            {
              "name" : "hrdtm",
              "symbol" : "rasterV"
            }
          ],
          "azimuth": 315,
          "altitude": 60,
          "symbol" : "fhillshade"
        }
        defaultStyle = "default"
        styles = [
            {
                name = "greyscaleramp"
                title = "Greyscale Ramp"
                type = "colorrampconf"
                colors = ${color-ramps.slope}
                min-render = 0
                max-render = 127
                stops = 255
            },
            {
                name = "greyscalemap"
                title = "Greyscale Map"
                type = "colormapconf"
                color-map = ${color-maps.hillshade}
            }
        ]
    }
}

color-ramps = {
    "red-to-blue": [
        0x2A2E7FFF, 0x3D5AA9FF, 0x4698D3FF, 0x39C6F0FF,
        0x76C9B3FF, 0xA8D050FF, 0xF6EB14FF, 0xFCB017FF,
        0xF16022FF, 0xEE2C24FF, 0x7D1416FF
    ],
    "elevation": [
        0x375A91FF, 0x2D82B9FF, 0x78B978FF, 0x91C882FF, 0xB9DC91FF, 0xFFFFAAFF, 0xE6DC8CFF, 0xCDBE73FF, 0xB49B55FF, 0x9B7D37FF, 0x6E3C00FF, 0xA59678FF, 0xD7D7D7FF, 0xFFFFFFFF
    ],
    "greyscale": [
        0x000000FF, 0xA6A6A6FF
    ],
    "slope": [
        0x000000FF, 0xFFFFFFFF
    ]    
}

color-maps = {
...

in this example, the hillshade layer will render with the greyscaleramp but not the slope layer.