private void endKeyConstraint() {
    String className = ((StringBuilder) stack.pop()).toString().trim();
    Class c;
    try {
      c = InternalDataSerializer.getCachedClass(className);
    } catch (Exception ex) {
      throw new CacheXmlException(
          String.format("Could not load key-constraint class: %s",
              className),
          ex);
    }
    // The region attributes should be on top of the stack
    RegionAttributesCreation attrs = peekRegionAttributesContext("key-constraint");
    attrs.setKeyConstraint(c);
  }
When a <code>key-constraint</code> element is finished, the name of the class should be on top
of the stack.

@throws CacheXmlException If the key constraint class cannot be loaded
geode-core/src/main/java/org/apache/geode/internal/cache/xmlcache/CacheXmlParser.java