Index: trunk/src/org/openstreetmap/josm/actions/AbstractMergeAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/AbstractMergeAction.java	(revision 15785)
+++ trunk/src/org/openstreetmap/josm/actions/AbstractMergeAction.java	(revision 15786)
@@ -121,28 +121,4 @@
 
     /**
-     * Ask user to choose the target layer.
-     * @param targetLayers list of candidate target layers.
-     * @return the chosen layer
-     * @deprecated to be removed
-     */
-    @Deprecated
-    protected static Layer askTargetLayer(List<Layer> targetLayers) {
-        return askTargetLayer(targetLayers, false, null, false, tr("Merge")).selectedTargetLayer;
-    }
-
-    /**
-     * Ask user to choose the target layer and shows a checkbox.
-     * @param targetLayers list of candidate target layers.
-     * @param checkbox The text of the checkbox shown to the user.
-     * @param checkboxDefault whether the checkbox is ticked by default
-     * @return The {@link TargetLayerDialogResult} containing the chosen target layer and the state of the checkbox
-     * @deprecated to be removed
-     */
-    @Deprecated
-    protected static TargetLayerDialogResult<Layer> askTargetLayer(List<Layer> targetLayers, String checkbox, boolean checkboxDefault) {
-        return askTargetLayer(targetLayers, true, checkbox, checkboxDefault, tr("Merge"));
-    }
-
-    /**
      * Ask user to choose the target layer and shows a checkbox.
      * @param targetLayers list of candidate target layers.
@@ -154,5 +130,5 @@
      * @since 15450
      */
-    protected static TargetLayerDialogResult<Layer> askTargetLayer(List<Layer> targetLayers, boolean showCheckbox,
+    protected static TargetLayerDialogResult<Layer> askTargetLayer(List<? extends Layer> targetLayers, boolean showCheckbox,
             String checkbox, boolean checkboxDefault, String buttonText) {
         return askTargetLayer(targetLayers.toArray(new Layer[0]),
Index: trunk/src/org/openstreetmap/josm/actions/MergeLayerAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/MergeLayerAction.java	(revision 15785)
+++ trunk/src/org/openstreetmap/josm/actions/MergeLayerAction.java	(revision 15786)
@@ -52,5 +52,5 @@
      * @since 11885 (return type)
      */
-    protected Future<?> doMerge(List<Layer> targetLayers, final Collection<Layer> sourceLayers) {
+    protected Future<?> doMerge(List<? extends Layer> targetLayers, final Collection<? extends Layer> sourceLayers) {
         final boolean onlygpx = targetLayers.stream().noneMatch(l -> !(l instanceof GpxLayer));
         final TargetLayerDialogResult<Layer> res = askTargetLayer(targetLayers, onlygpx,
@@ -125,5 +125,5 @@
      * @since 11885 (return type)
      */
-    public Future<?> merge(List<Layer> sourceLayers) {
+    public Future<?> merge(List<? extends Layer> sourceLayers) {
         return doMerge(sourceLayers, sourceLayers);
     }