Graph: fix for legend values min & max, avg & current when series only has null values, Closes #923

src/app/components/timeSeries.js

@@ -63,8 +63,10 @@ function (_, kbn) {
     this.yaxis = this.info.yaxis;
 
     this.stats.total = 0;
-    this.stats.max = -212312321312;
-    this.stats.min = 212312321312;
+    this.stats.max = Number.MIN_VALUE;
+    this.stats.min = Number.MAX_VALUE;
+    this.stats.avg = null;
+    this.stats.current = null;
 
     var ignoreNulls = fillStyle === 'connected';
     var nullAsZero = fillStyle === 'null as zero';
@@ -101,6 +103,9 @@ function (_, kbn) {
       this.stats.timeStep = result[1][0] - result[0][0];
     }
 
+    if (this.stats.max === Number.MIN_VALUE) { this.stats.max = null; }
+    if (this.stats.min === Number.MAX_VALUE) { this.stats.min = null; }
+
     if (result.length) {
       this.stats.avg = (this.stats.total / result.length);
       this.stats.current = result[result.length-1][1];