Add missing API test

Author: garydgregory

src/test/java/org/apache/commons/cli/OptionTest.java

@@ -104,6 +104,12 @@ private Option roundTrip(final Option o) throws IOException, ClassNotFoundExcept
         return (Option) ois.readObject();
     }
 
+    @Test
+    public void testAddValue() {
+        final Option option = new Option("f", null);
+        assertThrows(UnsupportedOperationException.class, () -> option.addValue(""));
+    }
+
     @Test
     public void testBuilderInsufficientParams1() {
         assertThrows(IllegalArgumentException.class, () -> Option.builder().desc("desc").build());