@Override
  public Object removeAttribute(String attr) {
    Object obj = attributes.remove(attr);
    deltas.put(attr, new DeltaEvent(false, attr, null));
    return obj;
  }
{@inheritDoc} Remove an attribute, setting the dirty flag. The changes are flushed at the end
of filter processing.
extensions/geode-modules-session-internal/src/main/java/org/apache/geode/modules/session/internal/filter/attributes/DeltaQueuedSessionAttributes.java