@Override
  public void stop(CoprocessorEnvironment env) throws IOException {
    // Nothing to do.
  }
Test coprocessor endpoint that always returns {@code null} for requests to the last region in the
table. This allows tests to provide assurance of correct {@code null} handling for response
values.
hbase-endpoint/src/test/java/org/apache/hadoop/hbase/coprocessor/ColumnAggregationEndpointNullResponse.java