content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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.apache.calcite.schema.lookup;
  
  import com.google.common.collect.ImmutableSet;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Set;
  
  /**
   * This class implements an empty Lookup.
   *
   * <p>This class returns null for any call to {@code EmptyLookup.get(String)} or
   * {@code EmptyLookup.getIgnoreCase(String)}.
   *
   * @param <T> Element type
   */
  class EmptyLookup<T> implements Lookup<T> {
  
    static final Lookup<?> INSTANCE = new EmptyLookup<>();
  
    @Override public @Nullable T get(String name) {
      return null;
    }
  
    @Override public @Nullable Named<T> getIgnoreCase(String name) {
      return null;
    }
  
    @Override public Set<String> getNames(LikePattern pattern) {
      return ImmutableSet.of();
    }
  }
  