Index: trunk/src/org/openstreetmap/josm/data/gpx/GpxData.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/gpx/GpxData.java	(revision 16941)
+++ trunk/src/org/openstreetmap/josm/data/gpx/GpxData.java	(revision 16942)
@@ -724,5 +724,5 @@
                 .mapToLong(WayPoint::getTimeInMillis)
                 .summaryStatistics();
-        return statistics.getCount() == 0
+        return statistics.getCount() == 0 || (statistics.getMin() == 0 && statistics.getMax() == 0)
                 ? null
                 : new Date[]{new Date(statistics.getMin()), new Date(statistics.getMax())};
Index: trunk/src/org/openstreetmap/josm/gui/layer/gpx/ChooseTrackVisibilityAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/gpx/ChooseTrackVisibilityAction.java	(revision 16941)
+++ trunk/src/org/openstreetmap/josm/gui/layer/gpx/ChooseTrackVisibilityAction.java	(revision 16942)
@@ -325,5 +325,5 @@
             if (c instanceof JComponent) {
                 JComponent jc = (JComponent) c;
-                jc.setToolTipText(getValueAt(row, col).toString());
+                jc.setToolTipText(String.valueOf(getValueAt(row, col)));
                 if (content.length > row
                         && content[row].length > 5