[FIXED JENKINS-21239] Trend Graph NPE when no builds

core/src/main/java/hudson/model/Job.java

@@ -1216,7 +1216,7 @@ public abstract class Job<JobT extends Job<JobT, RunT>, RunT extends Run<JobT, R
     }
 
     public Graph getBuildTimeGraph() {
-        return new Graph(getLastBuild().getTimestamp(),500,400) {
+        return new Graph(getLastBuildTime(),500,400) {
             @Override
             protected JFreeChart createGraph() {
                 class ChartLabel implements Comparable<ChartLabel> {
@@ -1350,6 +1350,16 @@ public abstract class Job<JobT extends Job<JobT, RunT>, RunT extends Run<JobT, R
         };
     }
 
+    private Calendar getLastBuildTime() {
+        final RunT lastBuild = getLastBuild();
+        if (lastBuild ==null) {
+            final GregorianCalendar neverBuiltCalendar = new GregorianCalendar();
+            neverBuiltCalendar.setTimeInMillis(0);
+            return neverBuiltCalendar;
+        }
+        return lastBuild.getTimestamp();
+    }
+
     /**
      * Renames this job.
      */