@Override
  public Object setUserAttribute(Object userAttribute) {
    return region.getEntryUserAttributes().put(getKey(), userAttribute);
  }
Returns the entry's RegionEntry if it "checks" out. The check is to see if the region entry
still exists.

@throws EntryNotFoundException if the RegionEntry has been removed.
geode-core/src/main/java/org/apache/geode/internal/cache/ExpiryRegionEntry.java