Return null when trying to randomize empty enums

Resolves #393

README.md

@@ -234,6 +234,7 @@ If you have any question, suggestion, or feedback, do not hesitate to use the [G
 * [Weronika Redlarska](https://github.com/weronika-redlarska)
 * [Konstantin Lutovich](https://github.com/lutovich)
 * [Steven_Van_Ophem](https://github.com/stevenvanophem)
+* [Jean-Michel Leclercq](https://github.com/LeJeanbono)
 
 Thank you all for your contributions!
 

easy-random-core/src/main/java/org/jeasy/random/randomizers/misc/EnumRandomizer.java

@@ -117,6 +117,9 @@ public static <E extends Enum<E>> EnumRandomizer<E> aNewEnumRandomizer(final Cla
      */
     @Override
     public E getRandomValue() {
+        if (enumConstants.isEmpty()) {
+            return null;
+        }
         int randomIndex = random.nextInt(enumConstants.size());
         return enumConstants.get(randomIndex);
     }

easy-random-core/src/test/java/org/jeasy/random/randomizers/misc/EnumRandomizerTest.java

@@ -60,4 +60,12 @@ void should_return_a_value_different_from_the_excluded_one() {
     void should_throw_an_exception_when_all_values_are_excluded() {
         assertThatThrownBy(() -> aNewEnumRandomizer(Gender.class, Gender.values())).isInstanceOf(IllegalArgumentException.class);
     }
+
+    public enum Empty {}
+
+    @Test
+    public void should_return_null_for_empty_enum() {
+        Empty randomElement = aNewEnumRandomizer(Empty.class).getRandomValue();
+        assertThat(randomElement).isNull();
+    }
 }