private boolean findAndSaveExistingEntry() {
    RegionEntry re = getRegionMap().getEntry(getEvent());
    if (isOnlyExisting() && !entryExists(re)) {
      setRegionEntry(null);
      return false;
    }
    setRegionEntry(re);
    return true;
  }
If an existing one is found, save it by calling setRegionEntry.

@return false if an existing entry was not found and this put requires
        an existing one; otherwise returns true.
geode-core/src/main/java/org/apache/geode/internal/cache/map/AbstractRegionMapPut.java