fix empty bin histogram2d hover labels content

- this removed the annoying `x: NaN` from histogram2d
  hover labels

Author: etpinard

src/traces/histogram2d/calc.js

@@ -205,11 +205,13 @@ function getRanges(edges, uniqueVals, gapLow, gapHigh, ax, calendar) {
     var i;
     var len = edges.length - 1;
     var out = new Array(len);
-    if(uniqueVals) {
-        for(i = 0; i < len; i++) out[i] = [uniqueVals[i], uniqueVals[i]];
-    } else {
-        var roundFn = getBinSpanLabelRound(gapLow, gapHigh, edges, ax, calendar);
-        for(i = 0; i < len; i++) out[i] = [roundFn(edges[i]), roundFn(edges[i + 1], true)];
+    var roundFn = getBinSpanLabelRound(gapLow, gapHigh, edges, ax, calendar);
+
+    for(i = 0; i < len; i++) {
+        var v = (uniqueVals || [])[i];
+        out[i] = v === undefined ?
+            [roundFn(edges[i]), roundFn(edges[i + 1], true)] :
+            [v, v];
     }
     return out;
 }

test/jasmine/tests/histogram2d_test.js

@@ -479,5 +479,53 @@ describe('Test histogram2d hover:', function() {
             .catch(failTest)
             .then(done);
         });
+
+        it('shows the data range when bins have no value in it', function(done) {
+            function _check(msg, xpx, ypx, lines) {
+                _hover(xpx, ypx);
+                assertHoverLabelContent({nums: lines.join('\n')}, msg);
+            }
+
+            Plotly.newPlot('graph', [{
+                type: 'histogram2d',
+                x: [18.78],
+                y: [3],
+                xbins: {
+                    start: 0,
+                    end: 55,
+                    size: 5
+                },
+                ybins: {
+                    start: 0,
+                    end: 11,
+                    size: 1
+                }
+            }], {
+                width: 400,
+                height: 400,
+                margin: {l: 0, t: 0, r: 0, b: 0}
+            })
+            .then(function() {
+                expect(gd.calcdata[0][0].xRanges).toBeCloseTo2DArray([
+                    [0, 4], [5, 9], [10, 14],
+                    [18.78, 18.78],
+                    [20, 24], [25, 29], [30, 34],
+                    [35, 39], [40, 44], [45, 49], [50, 54]
+                ], 2, 'x-bins with some spread');
+                expect(gd.calcdata[0][0].yRanges).toBeCloseTo2DArray([
+                    [0, 0], [1, 1], [2, 2], [3, 3], [4, 4], [5, 5],
+                    [6, 6], [7, 7], [8, 8], [9, 9], [10, 10]
+                ], 2, 'y-bins with single values');
+
+                _check('on pt (!)', 100, 275, ['x: 18.78', 'y: 3', 'z: 1']);
+                _check('on x of pt, above it', 100, 200, ['x: 18.78', 'y: 5', 'z: 0']);
+                _check('off left/top of pt', 50, 100, ['x: 5 - 9', 'y: 8', 'z: 0']);
+                _check('off right/top of pt', 300, 100, ['x: 50 - 54', 'y: 8', 'z: 0']);
+                _check('off left/bottom of pt', 50, 325, ['x: 5 - 9', 'y: 2', 'z: 0']);
+                _check('off right/bottom of pt', 300, 325, ['x: 50 - 54', 'y: 2', 'z: 0']);
+            })
+            .catch(failTest)
+            .then(done);
+        });
     });
 });