Flex list: explicitly throw on null elements.

Author: greenrobot-team

objectbox-java/src/main/java/io/objectbox/converter/FlexObjectConverter.java

@@ -142,6 +142,9 @@ private void addVector(FlexBuffersBuilder builder, String vectorKey, List<Object
         int vectorStart = builder.startVector();
 
         for (Object item : list) {
+            if (item == null) {
+                throw new IllegalArgumentException("List elements must not be null");
+            }
             if (item instanceof Map) {
                 //noinspection unchecked
                 addMap(builder, null, (Map<Object, Object>) item);

tests/objectbox-java-test/src/test/java/io/objectbox/converter/FlexObjectConverterTest.java

@@ -9,6 +9,7 @@
 import java.util.Map;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 
 /**
  * Tests {@link FlexObjectConverter} basic types and flexible list conversion.
@@ -51,6 +52,14 @@ public void list_works() {
         // Java Float is returned as Double, so expect Double.
         list.set(3, (double) 1.3f);
         assertEquals(list, restoredList);
+
+        // list with null element
+        list.add(null);
+        IllegalArgumentException exception = assertThrows(
+                IllegalArgumentException.class,
+                () -> convertAndBack(list, converter)
+        );
+        assertEquals("List elements must not be null", exception.getMessage());
     }
 
     @SuppressWarnings("unchecked")