Showing details of multi-value metric throws an exception for the first time

[mgencur]

Steps to reproduce:

• create a test execution with "Multi-value" metric
• go to the UI, open the test execution, and click on "Multi-value" link next to the metric name
• for the first time the following exception is thrown, when I return back and click on the link again, the chart is displayed correctly

Exception on server side:
Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:101)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
... 76 more
Caused by: java.lang.NullPointerException
at org.perfrepo.web.controller.TestExecutionController.computeMultiValueChart(TestExecutionController.java:545)
at org.perfrepo.web.controller.TestExecutionController.showMultiValue(TestExecutionController.java:537)
at sun.reflect.GeneratedMethodAccessor620.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at javax.el.ELUtil.invokeMethod(ELUtil.java:300)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:415)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:256)
at com.sun.el.parser.AstValue.invoke(AstValue.java:285)
at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:304)
at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:40)
at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:50)
at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:40)
at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:50)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
... 77 more