remove not required SuppressWarnings annotation

Author: davidmoten

src/main/java/com/microsoft/graph/serializer/DefaultSerializer.java

@@ -154,7 +154,6 @@ private JsonObject getChildAdditionalData(IJsonBackedObject serializableObject,
 
 				// If the object is a HashMap, iterate through its children
 				if (fieldObject instanceof HashMap) {
-					@SuppressWarnings("unchecked")
                     HashMap<String, Object> serializableChildren = (HashMap<String, Object>) fieldObject;
 					Iterator<Entry<String, Object>> it = serializableChildren.entrySet().iterator();
 

src/test/java/com/microsoft/graph/serializer/DefaultSerializerTests.java

@@ -103,16 +103,21 @@ public void testDeserializeDerivedType() throws Exception {
 	}
 
     @Test
-    public void testSerializerCanSerializeVoid() {
+    public void testSerializerCanSerializeVoidWithoutEmittingWarning() {
+        // Unfortunately does not assert for existence of Java 9 illegal access warnings
+        // which seem to written to the console without use of System.err/System.out (so cannot be captured AFAIK). 
+        // @davidmoten
         final DefaultSerializer serializer = new DefaultSerializer(new DefaultLogger());
-        Test1 t = new Test1();
+        HasVoidMember t = new HasVoidMember();
         String json = serializer.serializeObject(t);
         // this line will emit a warning from Java 9 about illegal access to the constructor of Void 
         // if gson TypeAdapterFactory is not handling Void properly
-        serializer.deserializeObject(json, Test1.class);
+        HasVoidMember t2 = serializer.deserializeObject(json, HasVoidMember.class);
+        assertEquals(t.x, t2.x);
+        assertEquals(t.y, t2.y);
     }
 
-  public static final class Test1 {
+  public static final class HasVoidMember {
       @SerializedName("x")
       @Expose
       int x = 1;