Fix single graph bug in chart.js4, a=chris

diff --git a/src/scripts/chart.js b/src/scripts/chart.js
index 09c8f00df..b48c291a3 100644
--- a/src/scripts/chart.js
+++ b/src/scripts/chart.js
@@ -240,7 +240,7 @@ function Chart(chart_id, data)
         self.renderAxes();
         num_graphs = 1;
         var graph_data = {};
-        if (data.num_graphs === 'undefined') {
+        if (!data.num_graphs) {
             graph_data[0] = data;
         } else {
             graph_data = data.graphs;
@@ -248,7 +248,7 @@ function Chart(chart_id, data)
         }
         var x_values;
         for (var i = 0; i < num_graphs; i++) {
-            if (data.x_values === 'undefined') {
+            if (!data.x_values) {
                 x_values = graph_data[i];
             } else {
                 x_values = data.x_values;
@@ -265,7 +265,7 @@ function Chart(chart_id, data)
             var height = self.height - self.y_padding - self.tick_length;
             var x = self.x_padding;
             for (var x_key in x_values) {
-                if (graph_data[i][x_key] !== 'undefined') {
+                if (graph_data[i][x_key]) {
                     y = self.tick_length + height *
                         (1 - (graph_data[i][x_key] -
                         self.min_value)/self.range);
@@ -284,7 +284,7 @@ function Chart(chart_id, data)
         self.drawPointGraph();
         num_graphs = 1;
         var graph_data = {};
-        if (data.num_graphs === 'undefined') {
+        if (!data.num_graphs) {
             graph_data[0] = data;
         } else {
             graph_data = data.graphs;
@@ -293,7 +293,7 @@ function Chart(chart_id, data)
         var x_values;
         var dash_state = 0;
         for (var i = 0; i < num_graphs; i++) {
-            if (data.x_values === 'undefined') {
+            if (!data.x_values) {
                 x_values = graph_data[i];
             } else {
                 x_values = data.x_values;
@@ -319,7 +319,7 @@ function Chart(chart_id, data)
             var height = self.height - self.y_padding  - self.tick_length;
             var first_time = true;
             for (var x_key in x_values) {
-                if (graph_data[i][x_key] !== 'undefined') {
+                if (graph_data[i][x_key]) {
                     y = self.tick_length + height *
                         (1 - (graph_data[i][x_key] - self.min_value)
                         / self.range);
@@ -345,7 +345,7 @@ function Chart(chart_id, data)
         self.renderAxes();
         num_graphs = 1;
         graph_data = {};
-        if (data.num_graphs === 'undefined') {
+        if (!data.num_graphs) {
             graph_data[0] = data;
         } else {
             graph_data = data.graphs;
@@ -353,7 +353,7 @@ function Chart(chart_id, data)
         }
         var x_values;
         for (var i = 0; i < num_graphs; i++) {
-            if (data.x_values === 'undefined') {
+            if (!data.x_values) {
                 x_values = graph_data[i];
             } else {
                 x_values = data.x_values;
@@ -370,7 +370,7 @@ function Chart(chart_id, data)
             var height = self.height - self.y_padding - self.tick_length;
             var x = self.x_padding + i * (dx/num_graphs)
             for (x_key in x_values) {
-                if (graph_data[i][x_key] !== 'undefined') {
+                if (graph_data[i][x_key]) {
                     y = self.tick_length + height *
                         (1 - (graph_data[i][x_key] - self.min_value)
                         / self.range);