Index: trunk/src/org/openstreetmap/josm/data/validation/tests/DuplicateNode.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/validation/tests/DuplicateNode.java	(revision 11004)
+++ trunk/src/org/openstreetmap/josm/data/validation/tests/DuplicateNode.java	(revision 11007)
@@ -32,4 +32,5 @@
 import org.openstreetmap.josm.data.validation.TestError;
 import org.openstreetmap.josm.gui.progress.ProgressMonitor;
+import org.openstreetmap.josm.tools.CheckParameterUtil;
 import org.openstreetmap.josm.tools.MultiMap;
 
@@ -86,4 +87,11 @@
     }
 
+    private static class DuplicateNodeTestError extends TestError {
+        DuplicateNodeTestError(Test parentTest, Severity severity, String msg, int code, Set<OsmPrimitive> primitives) {
+            super(parentTest, severity, tr("Duplicated nodes"), tr(msg), msg, code, primitives);
+            CheckParameterUtil.ensureThat(!primitives.isEmpty(), "Empty primitives: " + msg);
+        }
+    }
+
     protected static final int DUPLICATE_NODE = 1;
     protected static final int DUPLICATE_NODE_MIXED = 2;
@@ -173,6 +181,6 @@
         // check whether we have multiple nodes at the same position with the same tag set
         for (Iterator<Map<String, String>> it = mm.keySet().iterator(); it.hasNext();) {
-            Map<String, String> tagSet = it.next();
-            if (mm.get(tagSet).size() > 1) {
+            Set<OsmPrimitive> primitives = mm.get(it.next());
+            if (primitives.size() > 1) {
 
                 for (String type: TYPES) {
@@ -180,5 +188,5 @@
                 }
 
-                for (OsmPrimitive p : mm.get(tagSet)) {
+                for (OsmPrimitive p : primitives) {
                     if (p.getType() == OsmPrimitiveType.NODE) {
                         Node n = (Node) p;
@@ -203,122 +211,86 @@
                 }
 
-                int nbType = 0;
-                for (Entry<String, Boolean> entry: typeMap.entrySet()) {
-                    if (entry.getValue()) {
-                        nbType++;
-                    }
-                }
+                long nbType = typeMap.entrySet().stream().filter(Entry::getValue).count();
 
                 if (nbType > 1) {
-                    String msg = marktr("Mixed type duplicated nodes");
-                    errors.add(new TestError(
+                    errors.add(new DuplicateNodeTestError(
                             parentTest,
                             Severity.WARNING,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                            marktr("Mixed type duplicated nodes"),
                             DUPLICATE_NODE_MIXED,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("highway")) {
-                    String msg = marktr("Highway duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Highway duplicated nodes"),
                             DUPLICATE_NODE_HIGHWAY,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("railway")) {
-                    String msg = marktr("Railway duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Railway duplicated nodes"),
                             DUPLICATE_NODE_RAILWAY,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("waterway")) {
-                    String msg = marktr("Waterway duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Waterway duplicated nodes"),
                             DUPLICATE_NODE_WATERWAY,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("boundary")) {
-                    String msg = marktr("Boundary duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Boundary duplicated nodes"),
                             DUPLICATE_NODE_BOUNDARY,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("power")) {
-                    String msg = marktr("Power duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Power duplicated nodes"),
                             DUPLICATE_NODE_POWER,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("natural")) {
-                    String msg = marktr("Natural duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Natural duplicated nodes"),
                             DUPLICATE_NODE_NATURAL,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("building")) {
-                    String msg = marktr("Building duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Building duplicated nodes"),
                             DUPLICATE_NODE_BUILDING,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else if (typeMap.get("landuse")) {
-                    String msg = marktr("Landuse duplicated nodes");
-                    errors.add(new TestError(
-                            parentTest,
-                            Severity.ERROR,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                    errors.add(new DuplicateNodeTestError(
+                            parentTest,
+                            Severity.ERROR,
+                            marktr("Landuse duplicated nodes"),
                             DUPLICATE_NODE_LANDUSE,
-                            mm.get(tagSet)
+                            primitives
                             ));
                 } else {
-                    String msg = marktr("Other duplicated nodes");
-                    errors.add(new TestError(
+                    errors.add(new DuplicateNodeTestError(
                             parentTest,
                             Severity.WARNING,
-                            tr("Duplicated nodes"),
-                            tr(msg),
-                            msg,
+                            marktr("Other duplicated nodes"),
                             DUPLICATE_NODE_OTHER,
-                            mm.get(tagSet)
-                            ));
-
+                            primitives
+                            ));
                 }
                 it.remove();
@@ -326,7 +298,5 @@
         }
 
-        // check whether we have multiple nodes at the same position with
-        // differing tag sets
-        //
+        // check whether we have multiple nodes at the same position with differing tag sets
         if (!mm.isEmpty()) {
             List<OsmPrimitive> duplicates = new ArrayList<>();