public static boolean has(TableDescriptor desc, Class<? extends Constraint> clazz) {
    return getKeyValueForClass(desc, clazz) != null;
  }
Check to see if the Constraint is currently set.
@param desc  {@link TableDescriptor} to check
@param clazz {@link Constraint} class to check for.
@return <tt>true</tt> if the {@link Constraint} is present, even if it is disabled.
        <tt>false</tt> otherwise.
hbase-server/src/main/java/org/apache/hadoop/hbase/constraint/Constraints.java