Index: /trunk/src/org/openstreetmap/josm/gui/widgets/HistoryComboBox.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/widgets/HistoryComboBox.java	(revision 18127)
+++ /trunk/src/org/openstreetmap/josm/gui/widgets/HistoryComboBox.java	(revision 18128)
@@ -6,5 +6,4 @@
 import javax.swing.text.JTextComponent;
 
-import org.openstreetmap.josm.data.tagging.ac.AutoCompletionItem;
 import org.openstreetmap.josm.gui.tagging.ac.AutoCompletingComboBox;
 import org.openstreetmap.josm.spi.preferences.Config;
@@ -56,12 +55,5 @@
      */
     public void addCurrentItemToHistory() {
-        Object item = getEditor().getItem();
-        if (item instanceof String) {
-            model.addElement((String) item);
-        } else if (item instanceof AutoCompletionItem) {
-            model.addElement((AutoCompletionItem) item);
-        } else {
-            throw new IllegalArgumentException(item.getClass().getSimpleName() + " is not supported in addCurrentItemToHistory");
-        }
+        model.addElement(getEditor().getItem().toString());
     }
 
Index: /trunk/test/unit/org/openstreetmap/josm/gui/widgets/HistoryComboBoxTest.java
===================================================================
--- /trunk/test/unit/org/openstreetmap/josm/gui/widgets/HistoryComboBoxTest.java	(revision 18127)
+++ /trunk/test/unit/org/openstreetmap/josm/gui/widgets/HistoryComboBoxTest.java	(revision 18128)
@@ -4,5 +4,4 @@
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.util.stream.Stream;
@@ -22,5 +21,5 @@
 class HistoryComboBoxTest {
     static Stream<Arguments> testNonRegression21203() {
-        return Stream.of(Arguments.of("Hello world"), Arguments.of(new AutoCompletionItem("Hello world2")));
+        return Stream.of(Arguments.of("Hello world"), Arguments.of(new AutoCompletionItem("Hello world2")), Arguments.of(new Double(42)));
     }
 
@@ -39,16 +38,10 @@
     }
 
-    /**
-     * This ensures that we do throw on unknown objects for #21203
-     */
     @Test
-    void testNonRegression21203Throws() {
+    void testEmptyEditor() {
         final HistoryComboBox historyComboBox = new HistoryComboBox();
-        // Sanity check
-        assertEquals(0, historyComboBox.getModel().getSize());
-        historyComboBox.getEditor().setItem(new Object());
-        IllegalArgumentException illegalArgumentException = assertThrows(IllegalArgumentException.class,
-                historyComboBox::addCurrentItemToHistory);
-        assertEquals("Object is not supported in addCurrentItemToHistory", illegalArgumentException.getMessage());
+        assertDoesNotThrow(historyComboBox::addCurrentItemToHistory);
+        historyComboBox.getEditor().setItem(null);
+        assertDoesNotThrow(historyComboBox::addCurrentItemToHistory);
     }
 }