code: public <T> T get(final Object key, final Class<T> clazz) {
          notNull("clazz", clazz);
          return clazz.cast(documentAsMap.get(key));
      }
docs: Gets the value of the given key, casting it to the given {@code Class<T>}.  This is useful to avoid having casts in client code,
  though the effect is the same.  So to get the value of a key that is of type String, you would write {@code String name =
  doc.get("name", String.class)} instead of {@code String name = (String) doc.get("x") }.
  
  @param key   the key
  @param clazz the non-null class to cast the value to
  @param <T>   the type of the class
  @return the value of the given key, or null if the instance does not contain this key.
  @throws ClassCastException if the value of the given key is not of type T