ModeledCache attempts to deserialize empty ZNodes on deletion, resulting in exceptions

When using the ModeledCache implementation, when a ZPath is deleted the implementation assumes that all ZNodes in the path contain a valid instance of the Model.

If intermediary paths have been created that do not contain a Model, the implementation is calling the Jackson deserialize method with null data, resulting in an exception.

Instead, the code should ensure there is valid data present prior to attempting to deserialize and call the "accept()" (callback) method on action NODE_REMOVED.

Example:

TestModel child1 = new TestModel("d", "e", "f", 1, BigInteger.ONE);
ZPath path1 = path.child("foo").child("bar").child("child1");

try (CachedModeledFramework<TestModel> client = ModeledFramework.wrap(async, modelSpec).cached())

{    CountDownLatch latch = new CountDownLatch(1);    client.listenable().addListener((t, p, s, m) -> latch.countDown());    client.start();    complete(client.withPath(path1).set(child1));    assertTrue(timing.awaitLatch(latch));    assertDoesNotThrow(() -> rawClient.delete().deletingChildrenIfNeeded().forPath(path.toString())); }

After calling "delete()", an exception is thrown:

ERROR org.apache.curator.x.async.modeled.TestCachedModeledFramework$$Lambda$409/0x0000000800e0c850 Could not process cache message [Curator-SafeNotifyService-0]
java.lang.IllegalArgumentException: argument "src" is null
at com.fasterxml.jackson.databind.ObjectReader._assertNotNull(ObjectReader.java:2120)