[FIX] web: undefined graph when pie chart has no data

Before this commit, a crash occured when the no content
helper was rendered on an pie chart without data.

addons/web/static/src/js/views/graph/graph_renderer.js

@@ -227,7 +227,10 @@ return AbstractRenderer.extend({
      * Helper function to set up data properly for the pieChart model in
      * nvd3.
      *
-     * @returns {nvd3 chart}
+     * returns undefined in the case of an non-embedded pie chart with no data.
+     * (all zero data included)
+     *.
+     * @returns {nvd3 chart|undefined}
      */
     _renderPieChart: function (stateData) {
         var self = this;
@@ -471,14 +474,16 @@ return AbstractRenderer.extend({
         }
         var chart = this['_render' + _.str.capitalize(this.state.mode) + 'Chart'](this.state.data);
 
-        // FIXME: When 'orient' is right for Y axis, horizontal lines aren't displayed correctly
-        chart.dispatch.on('renderEnd', function () {
-            $('.nv-y .tick > line').attr('x2', function (i, value) {
-                return Math.abs(value);
-            });
-        })
+        if (chart) {
+            // FIXME: When 'orient' is right for Y axis, horizontal lines aren't displayed correctly
+            chart.dispatch.on('renderEnd', function () {
+                $('.nv-y .tick > line').attr('x2', function (i, value) {
+                    return Math.abs(value);
+                });
+            })
 
-        chartResize(chart);
+            chartResize(chart);
+        }
 
         if (this.state.mode === 'pie' && this.isComparison) {
             // Render graph title
@@ -496,8 +501,9 @@ return AbstractRenderer.extend({
                 text: comparisonChartTitle,
             }));
             chartResize(comparisonChart);
-
-            chart.update();
+            if (chart) {
+                chart.update();
+            }
         } else if (this.title) {
             this.$('.o_graph_svg_container').last().prepend($('<label/>', {
                 text: this.title,

addons/web/static/tests/views/graph_tests.js

@@ -225,7 +225,7 @@ QUnit.module('Views', {
         });
     });
 
-    QUnit.test('no content helper', function (assert) {
+    QUnit.test('no content helper (bar chart)', function (assert) {
         assert.expect(2);
         this.data.foo.records = [];
 
@@ -244,6 +244,25 @@ QUnit.module('Views', {
         graph.destroy();
     });
 
+    QUnit.test('no content helper (pie chart)', function (assert) {
+        assert.expect(2);
+        this.data.foo.records =  []
+
+        var graph = createView({
+            View: GraphView,
+            model: "foo",
+            data: this.data,
+            arch: '<graph type="pie">' +
+                        '<field name="product_id"/>' +
+                '</graph>',
+        });
+        assert.strictEqual(graph.$('div.o_graph_svg_container svg.nvd3-svg').length, 0,
+            "should not contain a div with a svg element");
+        assert.strictEqual(graph.$('div.o_view_nocontent').length, 1,
+            "should display the no content helper");
+        graph.destroy();
+    });
+
     QUnit.test('no content helper after update', function (assert) {
         var done = assert.async();
         assert.expect(4);