Fix data.values interface

c3.js

@@ -6241,12 +6241,16 @@
             return [].concat(targetIds).indexOf(t.id) >= 0;
         });
     };
-    c3_chart_fn.data.shown = function (targetId) {
-        return this.internal.filterTargetsToShow(this.data(targetId));
+    c3_chart_fn.data.shown = function (targetIds) {
+        return this.internal.filterTargetsToShow(this.data(targetIds));
     };
     c3_chart_fn.data.values = function (targetId) {
-        var target = this.data(targetId);
-        return target[0] ? target[0].values.map(function (d) { return d.value; }) : null;
+        var targets, values = null;
+        if (targetId) {
+            targets = this.data(targetId);
+            values = targets[0] ? targets[0].values.map(function (d) { return d.value; }) : null;
+        }
+        return values;
     };
     c3_chart_fn.data.names = function (names) {
         return this.internal.updateDataAttributes('names', names);

spec/api.data-spec.js

@@ -87,6 +87,11 @@ describe('c3 api data', function () {
             });
         });
 
+        it('should return null when no args', function () {
+            var values = chart.data.values();
+            expect(values).toBeNull();
+        });
+
     });
 
     describe('data.names()', function () {

src/api.data.js

@@ -4,12 +4,16 @@ c3_chart_fn.data = function (targetIds) {
         return [].concat(targetIds).indexOf(t.id) >= 0;
     });
 };
-c3_chart_fn.data.shown = function (targetId) {
-    return this.internal.filterTargetsToShow(this.data(targetId));
+c3_chart_fn.data.shown = function (targetIds) {
+    return this.internal.filterTargetsToShow(this.data(targetIds));
 };
 c3_chart_fn.data.values = function (targetId) {
-    var target = this.data(targetId);
-    return target[0] ? target[0].values.map(function (d) { return d.value; }) : null;
+    var targets, values = null;
+    if (targetId) {
+        targets = this.data(targetId);
+        values = targets[0] ? targets[0].values.map(function (d) { return d.value; }) : null;
+    }
+    return values;
 };
 c3_chart_fn.data.names = function (names) {
     return this.internal.updateDataAttributes('names', names);