scripting: Do not return "multiple states" as label

In the presentation provider, events with no values, like arrows,
returned a "multiple states" string. Now it would return nothing.

Change-Id: I25ef00002e57c95287f4a709ef6a71aa279f18d6
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/151187
Tested-by: CI Bot
diff --git a/analyses/org.eclipse.tracecompass.incubator.scripting.ui/src/org/eclipse/tracecompass/incubator/internal/scripting/ui/views/timegraph/BasePresentationProvider.java b/analyses/org.eclipse.tracecompass.incubator.scripting.ui/src/org/eclipse/tracecompass/incubator/internal/scripting/ui/views/timegraph/BasePresentationProvider.java
index 384804a..f227229 100644
--- a/analyses/org.eclipse.tracecompass.incubator.scripting.ui/src/org/eclipse/tracecompass/incubator/internal/scripting/ui/views/timegraph/BasePresentationProvider.java
+++ b/analyses/org.eclipse.tracecompass.incubator.scripting.ui/src/org/eclipse/tracecompass/incubator/internal/scripting/ui/views/timegraph/BasePresentationProvider.java
@@ -132,7 +132,7 @@
         } else if (label != null) {
             return label;
         }
-        return "multiple state"; //$NON-NLS-1$
+        return null;
     }
 
     @Override