public boolean containsValueForKey(Object key) {
    return region.containsValueForKey(key);
  }
Getter for property modifiable. Since a QRegion as a collection represents an unmodifiable
facade on the values of this region, return false.

@return Value of property modifiable.
geode-core/src/main/java/org/apache/geode/cache/query/internal/QRegion.java