Index: /trunk/src/org/openstreetmap/josm/actions/JosmAction.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/actions/JosmAction.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/actions/JosmAction.java	(revision 6099)
@@ -76,4 +76,5 @@
             Main.registerActionShortcut(this, sc);
         }
+        if (tooltip==null) tooltip="";
         setTooltip(tooltip);
         if (getValue("toolbar") == null) {
Index: /trunk/src/org/openstreetmap/josm/gui/MapStatus.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/MapStatus.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/MapStatus.java	(revision 6099)
@@ -86,6 +86,6 @@
     public class BackgroundProgressMonitor implements ProgressMonitorDialog {
 
-        private String title;
-        private String customText;
+        private String title="";
+        private String customText="";
 
         private void updateText() {
Index: /trunk/src/org/openstreetmap/josm/gui/SideButton.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/SideButton.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/SideButton.java	(revision 6099)
@@ -88,4 +88,5 @@
         setActionCommand(name);
         addActionListener(actionListener);
+        if (tooltip==null) tooltip="";
         setToolTipText(tooltip);
         putClientProperty("help", "Dialog/"+property+"/"+name);
Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/LatLonDialog.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/LatLonDialog.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/LatLonDialog.java	(revision 6099)
@@ -205,4 +205,5 @@
     protected void setErrorFeedback(JosmTextField tf, String message) {
         tf.setBorder(BorderFactory.createLineBorder(Color.RED, 1));
+        if (message==null) message="";
         tf.setToolTipText(message);
         tf.setBackground(BG_COLOR_ERROR);
Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/properties/TagEditHelper.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/properties/TagEditHelper.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/properties/TagEditHelper.java	(revision 6099)
@@ -685,5 +685,7 @@
                     mainPanel.getActionMap().put(actionShortcutShiftKey, actionShift);
                     // Make the tag label clickable and set tooltip to the action description (this displays also the keyboard shortcut)
-                    tagLabel.setToolTipText((String) action.getValue(Action.SHORT_DESCRIPTION));
+                    String tooltip = (String) action.getValue(Action.SHORT_DESCRIPTION);
+                    if (tooltip==null) tooltip="";
+                    tagLabel.setToolTipText(tooltip);
                     tagLabel.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
                     tagLabel.addMouseListener(new MouseAdapter() {
Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/MemberTableCellRenderer.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/MemberTableCellRenderer.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/MemberTableCellRenderer.java	(revision 6099)
@@ -40,5 +40,5 @@
         setBorder(null);
         setIcon(null);
-        setToolTipText(null);
+        setToolTipText("");
     }
 
Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/SelectionTableCellRenderer.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/SelectionTableCellRenderer.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/SelectionTableCellRenderer.java	(revision 6099)
@@ -45,5 +45,5 @@
         setBorder(null);
         setIcon(null);
-        setToolTipText(null);
+        setToolTipText("");
     }
 
Index: /trunk/src/org/openstreetmap/josm/gui/download/BoundingBoxSelection.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/download/BoundingBoxSelection.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/download/BoundingBoxSelection.java	(revision 6099)
@@ -179,4 +179,5 @@
     protected void setErrorMessage(JosmTextField tf, String msg) {
         tf.setBorder(errorBorder);
+        if (msg==null) msg="";
         tf.setToolTipText(msg);
     }
Index: /trunk/src/org/openstreetmap/josm/gui/io/UploadStrategySelectionPanel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/io/UploadStrategySelectionPanel.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/io/UploadStrategySelectionPanel.java	(revision 6099)
@@ -397,4 +397,5 @@
         protected void setErrorFeedback(JosmTextField tf, String message) {
             tf.setBorder(BorderFactory.createLineBorder(Color.RED, 1));
+            if (message==null) message="";
             tf.setToolTipText(message);
             tf.setBackground(BG_COLOR_ERROR);
@@ -403,4 +404,5 @@
         protected void clearErrorFeedback(JosmTextField tf, String message) {
             tf.setBorder(UIManager.getBorder("TextField.border"));
+            if (message==null) message="";
             tf.setToolTipText(message);
             tf.setBackground(UIManager.getColor("TextField.background"));
Index: /trunk/src/org/openstreetmap/josm/gui/layer/gpx/ChooseTrackVisibilityAction.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/layer/gpx/ChooseTrackVisibilityAction.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/layer/gpx/ChooseTrackVisibilityAction.java	(revision 6099)
@@ -83,5 +83,6 @@
                 if (c instanceof JComponent) {
                     JComponent jc = (JComponent) c;
-                    jc.setToolTipText((String) getValueAt(row, col));
+                    String val=(String) getValueAt(row, col);
+                    jc.setToolTipText(val==null? "": val);
                 }
                 return c;
Index: /trunk/src/org/openstreetmap/josm/gui/tagging/TaggingPreset.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/tagging/TaggingPreset.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/tagging/TaggingPreset.java	(revision 6099)
@@ -310,4 +310,5 @@
                     if (icon != null)
                         setIconImage(icon.getImage());
+                    if (title==null) title="";
                     contentInsets = new Insets(10,5,0,5);
                     if (showNewRelation) {
Index: /trunk/src/org/openstreetmap/josm/gui/widgets/AbstractTextComponentValidator.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/widgets/AbstractTextComponentValidator.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/widgets/AbstractTextComponentValidator.java	(revision 6099)
@@ -51,5 +51,5 @@
             tc.setBorder(ERROR_BORDER);
             tc.setBackground(ERROR_BACKGROUND);
-            tc.setToolTipText(msg);
+            tc.setToolTipText(msg == null ? "" : msg);
             valid = false;
             this.msg = msg;
Index: /trunk/src/org/openstreetmap/josm/gui/widgets/ImageLabel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/widgets/ImageLabel.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/gui/widgets/ImageLabel.java	(revision 6099)
@@ -29,5 +29,5 @@
         add(new JLabel(ImageProvider.get("statusline/"+img+".png")), GBC.std().anchor(GBC.WEST).insets(0,1,1,0));
         add(tf = new JLabel(), GBC.std().fill(GBC.BOTH).anchor(GBC.WEST).insets(2,1,1,0));
-        setToolTipText(tooltip);
+        setToolTipText(tooltip==null ? "" : tooltip);
         this.charCount = charCount;
     }
Index: /trunk/src/org/openstreetmap/josm/tools/UrlLabel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/tools/UrlLabel.java	(revision 6098)
+++ /trunk/src/org/openstreetmap/josm/tools/UrlLabel.java	(revision 6099)
@@ -54,5 +54,5 @@
             setText("<html>" + description + "</html>");
             setCursor(null);
-            setToolTipText(null);
+            setToolTipText("");
         }
     }