fix null not mapped error

src/color_mode_discrete.js

@@ -65,6 +65,20 @@ export class ColorModeDiscrete {
   }
 
   getMatchedThreshold(value) {
+    if (value == null) {
+      if (this.panel.color.nullPointMode == 'as empty') {
+        // FIXME: make this explicit for user
+        // Right now this color never used because null as empty handles in getCardOpacity method.
+        return {
+          "color": "rgba(0,0,0,0)",
+          "value": "null",
+          "tooltip": "null",
+        }
+      } else {
+        value = 0;
+      }
+    }
+
     let thresholds = this.panel.color.thresholds;
     for (let k = 0; k < thresholds.length; k++) {
       if (value == thresholds[k].value) {

src/rendering.js

@@ -333,36 +333,6 @@ export default function link(scope, elem, attrs, ctrl) {
     return d3.scaleSequential(colorInterpolator).domain([start, end]);
   }
 
-// scale input range to discrete colors to draw a legend
-  function getDiscreteColorScale() {
-    let thresholds = panel.color.thresholds;
-
-    let thresholdValues = [];
-    let thresholdColors = [];
-    for (let i = 0; i < thresholds.length; i++) {
-      thresholdColors.push(thresholds[i].color);
-      thresholdValues.push(thresholds[i].value);
-    }
-
-    // TODO sort colors by value and index?
-
-    let thresholdScaler = (d) => {
-      for (let i = 0; i < thresholdValues.length; i++ ) {
-        if (d == thresholdValues[i]) {
-          return thresholdColors[i];
-        }
-      }
-      // Error if value not in thresholds
-      return 'rgba(0,0,0,1)';
-    };
-
-    // scale min-max to 0 - max-thrs-value
-    return function(d) {
-      return thresholdScaler(d);
-    }
-  }
-
-
   function setOpacityScale(maxValue) {
     if (panel.color.colorScale === 'linear') {
       opacityScale = d3.scaleLinear()