Fix single graph bug in chart.js5, a=chris

diff --git a/src/scripts/chart.js b/src/scripts/chart.js
index b48c291a3..8c2097e42 100644
--- a/src/scripts/chart.js
+++ b/src/scripts/chart.js
@@ -107,7 +107,7 @@ function Chart(chart_id, data)
         var val;
         var num_graphs = 1;
         var graph_data = {};
-        if (data.num_graphs === 'undefined') {
+        if (!data.num_graphs) {
             graph_data[0] = data;
         } else {
             graph_data = data.graphs;
@@ -200,14 +200,14 @@ function Chart(chart_id, data)
         }
         var num_graphs = 1;
         var graph_data = {};
-        if (data.num_graphs === 'undefined') {
+        if (!data.num_graphs) {
             graph_data[0] = data;
         } else {
             graph_data = data.graphs;
             num_graphs = data.num_graphs;
         }
         var x_values;
-        if (data.x_values === 'undefined') {
+        if (!data.x_values) {
             x_values = graph_data[0];
         } else {
             x_values = data.x_values;