@Test 
  public void canSerializeMapsWithNullablePrimitiveValues() throws SerDeException, IOException {
    String field = "{ \"name\":\"mapWithNulls\", \"type\": " +
            "{\"type\":\"map\", \"values\": [\"null\", \"boolean\"]} }";

    Map<String, Boolean> m = new HashMap<String, Boolean>();
    m.put("yes", true);
    m.put("no", false);
    m.put("maybe", null);
    GenericRecord r = serializeAndDeserialize(field, "mapWithNulls", m);

    Object result = r.get("mapWithNulls");
    assertEquals(m, result);
  }
Verify that we can serialize an avro value by taking one, running it through
the deser process and then serialize it again.
serde/src/test/org/apache/hadoop/hive/serde2/avro/TestAvroSerializer.java