@Override
  public String get(String key) {
    if (mutableConf != null) {
      String value = mutableConf.get(key);
      if (value != null) {
        return value;
      }
    }

    for (ImmutableConfigMap m : this.configs) {
      String value = m.get(key);
      if (value != null) {
        return value;
      }
    }
    return null;
  }
Add String map to config list. This map is generally created by HTableDescriptor or
HColumnDescriptor, but can be abstractly used. The added configuration overrides the previous
ones if there are name collisions.
@return this, for builder pattern
hbase-common/src/main/java/org/apache/hadoop/hbase/CompoundConfiguration.java