fix dodge identity (#902)

* avoid a crash on {r: {type:"identity"}}

* test

* check for scale existence

Co-authored-by: Mike Bostock <[email protected]>

Author: Fil

src/transforms/dodge.js

@@ -43,9 +43,9 @@ export function dodgeY(dodgeOptions = {}, options = {}) {
 function dodge(y, x, anchor, padding, options) {
   return initializer(options, function(data, facets, {[x]: X, r: R}, scales, dimensions) {
     if (!X) throw new Error(`missing channel: ${x}`);
-    X = coerceNumbers(valueof(X.value, X.scale !== undefined ? scales[X.scale] : identity));
+    X = coerceNumbers(valueof(X.value, scales[X.scale] || identity));
     const r = R ? undefined : this.r !== undefined ? this.r : options.r !== undefined ? number(options.r) : 3;
-    if (R) R = coerceNumbers(valueof(R.value, R.scale !== undefined ? scales[R.scale] : identity));
+    if (R) R = coerceNumbers(valueof(R.value, scales[R.scale] || identity));
     let [ky, ty] = anchor(dimensions);
     const compare = ky ? compareAscending : compareSymmetric;
     if (ky) ty += ky * ((R ? max(facets, I => max(I, i => R[i])) : r) + padding); else ky = 1;

src/transforms/hexbin.js

@@ -35,8 +35,8 @@ export function hexbin(outputs = {fill: "count"}, inputs = {}) {
 
     // Coerce the X and Y channels to numbers (so that null is properly treated
     // as an undefined value rather than being coerced to zero).
-    X = coerceNumbers(valueof(X.value, X.scale !== undefined ? scales[X.scale] : identity));
-    Y = coerceNumbers(valueof(Y.value, Y.scale !== undefined ? scales[Y.scale] : identity));
+    X = coerceNumbers(valueof(X.value, scales[X.scale] || identity));
+    Y = coerceNumbers(valueof(Y.value, scales[Y.scale] || identity));
 
     // Extract the values for channels that are eligible for grouping; not all
     // marks define a z channel, so compute one if it not already computed. If z