Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditor.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditor.java	(revision 9437)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditor.java	(revision 9438)
@@ -9,4 +9,5 @@
 import java.awt.Dimension;
 import java.awt.FlowLayout;
+import java.awt.GraphicsEnvironment;
 import java.awt.GridBagConstraints;
 import java.awt.GridBagLayout;
@@ -770,5 +771,7 @@
             for (OsmPrimitive p : primitivesToAdd) {
                 if (p instanceof Relation && orig.equals(p)) {
-                    warnOfCircularReferences(p);
+                    if (!GraphicsEnvironment.isHeadless()) {
+                        warnOfCircularReferences(p);
+                    }
                     continue;
                 } else if (MemberTableModel.hasMembersReferringTo(relation.getMembers(), Collections.singleton(p))
Index: /trunk/test/unit/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditorTest.java
===================================================================
--- /trunk/test/unit/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditorTest.java	(revision 9438)
+++ /trunk/test/unit/org/openstreetmap/josm/gui/dialogs/relation/GenericRelationEditorTest.java	(revision 9438)
@@ -0,0 +1,43 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.gui.dialogs.relation;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import java.util.Collections;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.openstreetmap.josm.JOSMFixture;
+import org.openstreetmap.josm.data.osm.Node;
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.osm.Relation;
+import org.openstreetmap.josm.data.osm.Way;
+
+/**
+ * Unit tests of {@link GenericRelationEditor} class.
+ */
+public class GenericRelationEditorTest {
+
+    /**
+     * Setup test.
+     */
+    @BeforeClass
+    public static void setUpBeforeClass() {
+        JOSMFixture.createUnitTestFixture().init();
+    }
+
+    /**
+     * Unit test of {@link GenericRelationEditor#addPrimitivesToRelation}.
+     */
+    @Test
+    public void testAddPrimitivesToRelation() {
+        assertNull(GenericRelationEditor.addPrimitivesToRelation(new Relation(1), Collections.<OsmPrimitive>emptyList()));
+        assertNull(GenericRelationEditor.addPrimitivesToRelation(new Relation(1), Collections.singleton(new Relation(1))));
+
+        assertNotNull(GenericRelationEditor.addPrimitivesToRelation(new Relation(1), Collections.singleton(new Node(1))));
+        assertNotNull(GenericRelationEditor.addPrimitivesToRelation(new Relation(1), Collections.singleton(new Way(1))));
+        assertNotNull(GenericRelationEditor.addPrimitivesToRelation(new Relation(1), Collections.singleton(new Relation(2))));
+    }
+
+}