@Deprecated
  public String getImplementationClassName() {
    return this.implementationClassName;
  }
@return Name of the class we will use when we construct a {@link BufferedMutator} instance or
        null if default implementation.
@deprecated Since 3.0.0, will be removed in 4.0.0. You can not set it any more as the
            implementation has to use too many internal stuffs in HBase.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/BufferedMutatorParams.java