code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC licenses this file
  // to you under the Apache License, Version 2.0 (the
  // "License"); you may not use this file except in compliance
  // with the License.  You may obtain a copy of the License at
  //
  //   http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing,
  // software distributed under the License is distributed on an
  // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, either express or implied.  See the License for the
  // specific language governing permissions and limitations
  // under the License.
  
  package org.openqa.selenium.grid.sessionmap;
  
  import org.openqa.selenium.NoSuchSessionException;
  import org.openqa.selenium.grid.data.Session;
  import org.openqa.selenium.remote.SessionId;
  import org.openqa.selenium.remote.tracing.Tracer;
  
  public class NullSessionMap extends SessionMap {
  
    public NullSessionMap(Tracer tracer) {
      super(tracer);
    }
  
    @Override
    public boolean add(Session session) {
      return false;
    }
  
    @Override
    public Session get(SessionId id) throws NoSuchSessionException {
      throw new NoSuchSessionException("No session found for " + id);
    }
  
    @Override
    public void remove(SessionId id) {
      // no-op
    }
  
    @Override
    public boolean isReady() {
      return true;
    }
  }
  