@Override
  public void set(String name, String value) {
    if (mutableConf == null) {
      // not thread safe
      mutableConf = new Configuration(false); // an empty configuration
    }
    mutableConf.set(name, value);
  }
Get the value of the <code>name</code>. If the key is deprecated, it returns the value of the
first key which replaces the deprecated key and is not null. If no such property exists, then
<code>defaultValue</code> is returned. The CompooundConfiguration does not do property
substitution. To do so we need Configuration.getProps to be protected or package visible.
Though in hadoop2 it is protected, in hadoop1 the method is private and not accessible. All of
the get* methods call this overridden get method.
@param name         property name.
@param defaultValue default value.
@return property value, or <code>defaultValue</code> if the property doesn't exist.
hbase-common/src/main/java/org/apache/hadoop/hbase/CompoundConfiguration.java