Index: trunk/src/org/openstreetmap/josm/gui/IconToggleButton.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/IconToggleButton.java	(revision 10383)
+++ trunk/src/org/openstreetmap/josm/gui/IconToggleButton.java	(revision 10384)
@@ -12,4 +12,5 @@
 import org.openstreetmap.josm.actions.ExpertToggleAction;
 import org.openstreetmap.josm.actions.ExpertToggleAction.ExpertModeChangeListener;
+import org.openstreetmap.josm.tools.CheckParameterUtil;
 import org.openstreetmap.josm.tools.Destroyable;
 
@@ -41,4 +42,5 @@
     public IconToggleButton(Action action, boolean isExpert) {
         super(action);
+        CheckParameterUtil.ensureParameterNotNull(action, "action");
         this.isExpert = isExpert;
         setText(null);
Index: trunk/src/org/openstreetmap/josm/gui/dialogs/ToggleDialog.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/dialogs/ToggleDialog.java	(revision 10383)
+++ trunk/src/org/openstreetmap/josm/gui/dialogs/ToggleDialog.java	(revision 10384)
@@ -716,5 +716,5 @@
 
         protected void rememberGeometry() {
-            if (detachedDialog != null) {
+            if (detachedDialog != null && detachedDialog.isShowing()) {
                 new WindowGeometry(detachedDialog).remember(preferencePrefix+".geometry");
             }
Index: trunk/src/org/openstreetmap/josm/tools/WindowGeometry.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/WindowGeometry.java	(revision 10383)
+++ trunk/src/org/openstreetmap/josm/tools/WindowGeometry.java	(revision 10384)
@@ -9,4 +9,5 @@
 import java.awt.GraphicsDevice;
 import java.awt.GraphicsEnvironment;
+import java.awt.IllegalComponentStateException;
 import java.awt.Insets;
 import java.awt.Point;
@@ -57,4 +58,5 @@
      *
      * @param window the window
+     * @throws IllegalComponentStateException if the window is not showing on the screen
      */
     public WindowGeometry(Window window) {