Index: /trunk/src/org/openstreetmap/josm/data/validation/TestError.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/validation/TestError.java	(revision 11134)
+++ /trunk/src/org/openstreetmap/josm/data/validation/TestError.java	(revision 11135)
@@ -140,4 +140,5 @@
         public Builder primitives(Collection<? extends OsmPrimitive> primitives) {
             CheckParameterUtil.ensureThat(this.primitives == null, "primitives already set");
+            CheckParameterUtil.ensureParameterNotNull(primitives, "primitives");
             this.primitives = primitives;
             if (this.highlighted == null) {
@@ -166,4 +167,5 @@
          */
         public Builder highlight(Collection<? extends OsmPrimitive> highlighted) {
+            CheckParameterUtil.ensureParameterNotNull(highlighted, "highlighted");
             this.highlighted = highlighted;
             return this;
@@ -178,4 +180,5 @@
          */
         public Builder highlightWaySegments(Collection<WaySegment> highlighted) {
+            CheckParameterUtil.ensureParameterNotNull(highlighted, "highlighted");
             this.highlighted = highlighted;
             return this;
@@ -190,4 +193,5 @@
          */
         public Builder highlightNodePairs(Collection<List<Node>> highlighted) {
+            CheckParameterUtil.ensureParameterNotNull(highlighted, "highlighted");
             this.highlighted = highlighted;
             return this;
Index: /trunk/src/org/openstreetmap/josm/data/validation/tests/MultipolygonTest.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/validation/tests/MultipolygonTest.java	(revision 11134)
+++ /trunk/src/org/openstreetmap/josm/data/validation/tests/MultipolygonTest.java	(revision 11135)
@@ -400,5 +400,5 @@
             for (OsmPrimitive p : primitives) {
                 if (!p.isIncomplete()) {
-                    return null;
+                    return primitives;
                 }
             }